Lighting unit

ABSTRACT

The invention relates to a backlight unit for liquid crystal displays, etc.; and its object is to provide a backlight unit not involving the problem that the emitted light leaks out of the optical waveguide, even when the space around the cold-cathode tubes in the light source unit for it is filled with a liquid of which the refractive index is nearly the same as that of the glass material that forms the outer wall of the cold-cathode tubes. The backlight unit comprises a housing  6  which houses cold-cathode tubes  2, 4  therein and of which the inner surface is coated with a light reflector  10;  a transparent liquid filled in the housing  6;  and an optical waveguide  1  made of a transparent substance and having a light-emitting surface S. The reflective surface of the light reflector  10  has a cross-section profile of X-T-U-V-W-Y, on which the light emitted by the cold-cathode tubes  2, 4  is reflected, and the thus-reflected light is led to the light-emitting surface S of the optical waveguide  1  at an incident angle not smaller than the critical angle to the surface S.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a backlight unit to be used in liquidcrystal displays, etc.

The invention also relates to a backlight unit in which the light sourceunit is filled with a transparent liquid.

The invention also relates to a reflector structure that realizeshigh-luminance and high-efficiency sidelight-type backlight units.

The invention also relates to a cold-cathode tube usable for a lightsource that receives essentially the fluorescence of the UV rays havingbeen emitted through discharge emission of mercury or the like and emitsvisible light, especially for the light source of that type for liquidcrystal displays.

2. Description of the Related Art

Recently, liquid crystal display panels have been rated highly in themarket, as they save space upon installation and save power duringoperation, and their applications are expanding not only for displays ofportable computers and monitors for portable televisions, but also formonitors of desk-top personal computers and flat televisions in domesticuse. The backlight unit for lighting the liquid crystal display surfaceof such a liquid crystal display panel from the back surface of thepanel includes two types; one being a direct-light-type unit thatcomprises a diffuser, a cold-cathode tube and a reflector all disposedjust below the back surface of a liquid crystal display panel, and theother being a sidelight-type unit that comprises a diffuser, an opticalwaveguide and a reflector all disposed just below the back surface of aliquid crystal display panel, in which a cold-cathode tube and areflector having a C-shaped or rectangularly U-shaped cross section aredisposed on both sides of the optical waveguide.

For downsizing them and saving space upon installation, the latter ispreferred to the former. However, the luminance of the formerdirect-light-type unit could be easily increased merely by increasingthe number of the cold-cathode tubes in the unit, but it is difficult toincrease the number of the cold-cathode tubes in the lattersidelight-type unit. It is therefore desired to increase the luminanceof sidelight-type backlight units by increasing the emission efficiencyof the units.

Prior Art 1

A sidelight-type backlight unit having a structure shown in FIG. 37A andFIG. 37B is generally used for liquid crystal display monitors. FIG. 37Ais a view of a backlight unit of that type seen on its emission side.FIG. 37B is a cross-sectional view of FIG. 37A cut along the line A—A.As illustrated, the backlight unit comprises an acrylic plate 100 (thisserves as an optical waveguide) with a light-scattering pattern 114formed on its back surface, and two cold-cathode tubes 102, 104 disposednearly in parallel with each other on and along one side of the acrylicplate 100. A reflector 110 (for this, an aluminum film is popularlyused) is provided to surround the two cold-cathode tubes 102, 104, andits one side is opened to the optical waveguide 100 facing thereto. Alsoon and along the other side of the optical waveguide 100 having the twocold-cathode tubes 102, 104 disposed on its one side, other twocold-cathode tubes 106, 108 are disposed nearly in parallel with eachother, and a reflector 112 is provided to surround the two cold-cathodetubes 106, 108 with its one side being opened to the optical waveguide100 facing thereto.

In case where the number of the cold-cathode tubes in the sidelight-typebacklight unit is increased for increasing the luminance of the unit, itproduces some problems. One problem is the efficiency in light emissionto the optical waveguide; and the other is the temperature of thecold-cathode tubes. Increasing the number of the cold-cathode tubes inthe limited space in the unit inevitably makes the tubes more tightlyadjacent to each other. As a result, in some region in the unit, theneighboring tubes will partly absorb the light emitted by them, therebylowering the emission efficiency of the unit. In addition, in the areain which such an increased number of cold-cathode tubes are tightlyaligned, the atmospheric temperature will increase, and if so, the tubesmust be cooled so as to keep them at a temperature at which they ensurethe maximum luminance.

In addition, the cold-cathode tubes in the unit involve by themselves afactor to lower the emission efficiency of the unit. As in FIG. 38, forexample, the light emitted from one point of a cold-cathode tube 108 ispartly reflected on the outer surface of the glass tube 136. In acold-cathode tube having, for example, an outer diameter of 2.6 mm andan inner diameter of 2.0 mm, the reflected light accounts for at least30% of the entire light emission from the tube. About 25% of thereflected light having reached the inner surface of the glass tube (forexample, on the point c and the point d in FIG. 38) will be absorbed bythe phosphor 138 coated on the inner surface of the glass tube or by themercury gas filled in the glass tube. In addition, when the light fromthe cold-cathode tube 108 enters the glass tube of the neighboringcold-cathode tube 106, about 25% of the incident light that reaches theinner surface of the glass tube (for example, on the point a and thepoint b in FIG. 38) will be absorbed by the phosphor 138 coated on theinner surface of the glass tube or by the mercury gas filled in theglass tube.

To solve the prior art problems noted above, a method is proposed, whichcomprises filling the outer peripheral space of a cold-cathode tube witha liquid of which the refractive index is nearly the same as that of theglass material that forms the outer wall of the cold-cathode tube.According to this method, the reflection on the outer surface of thecold-cathode tube can be reduced, and, in addition, the incident lightto the neighboring cold-cathode tube can be also reduced. Therefore, themethod will be effective for increasing the emission efficiency ofbacklight units. In addition, since the liquid filled in the spacearound the cold-cathode tube will act also as a coolant, anotheradvantage of the method is that the method does not involve the problemof temperature elevation even through a large number of cold-cathodetubes are packaged in the unit.

Prior Art 2

One conventional structure of a liquid crystal display with asidelight-type backlight unit used therein is described, for whichreferred to is FIG. 41. As illustrated, a backlight unit is disposedadjacent to the emission side of a liquid crystal panel 134. Thebacklight unit is composed of a light source unit that comprisescold-cathode tubes (fluorescent tubes) 102 to 108 and reflectors 110,112; and an optical waveguide unit that comprises a diffuser (opticalsheet) 130, an optical waveguide 100 and a reflector 132. As the casemay be, the diffuser 130 may have a multi-layered structure of pluralsheets, depending on the mode of light diffusion through the opticalwaveguide unit.

For increasing the luminance of the backlight unit, two cold-cathodetubes of 102 to 108 are disposed for each of the reflectors 110, 112,and the optical waveguide 100 therefore has two pairs of cold-cathodetubes on both of its sides. The light emitted by the cold-cathode tubes102 to 108 toward the optical waveguide 100 directly enters the opticalwaveguide 100 through its sides, and it is transmitted within thewaveguide while being almost entirely reflected on and around it. Thelight emitted by the cold-cathode tubes 102 to 108 toward the reflectors110, 112 is reflected by the reflectors 110, 112, and the thus-reflectedlight also enters the optical waveguide 100 through its sides and istransmitted within it like the direct light above.

Passing through the optical waveguide, a part of the light L1 goes outtoward the reflector 132 or toward the diffuser 130, and the light thatreaches the diffuser 130 passes through it while been diffusedtherethrough toward the liquid crystal panel 134. The light L2 thatreaches the reflector 132 is reflected by it, and then passes throughthe optical waveguide 100 to reach the diffuser 130. This is alsodiffused toward the liquid crystal panel 134. In this manner, the liquidcrystal panel 134 is illuminated by light diffused from two paths.

To meet the recent requirement for high-luminance backlight units,structures having a plurality of cold-cathode tubes disposed with onereflector are popular. In many cases, the shape of the reflector isdetermined depending on the external structure of the lighting unit andon the electric circuit and the wiring mode for the unit, for example,as in Japanese Patent Laid-Open No. 274185/1997.

Prior Art 3

An outline of the structure of the light source unit for conventional,direct-light-type backlight units is described with reference to FIG. 41and FIG. 43. The structure of the direct-light-type backlight unitdiffers from that of the sidelight-type backlight unit shown in FIG. 41in that, in the former, a plurality of straight light source tubes suchas cold-cathode tubes 102 a to 102 d or the like are disposed below thediffuser 130 to be a surface light-emitting member and they are coveredwith a reflector 110 around them, as in FIG. 43; while in the latter,the optical waveguide 100 is disposed below the diffuser 130 and thelight source units are on both sides of the optical waveguide 100, as inFIG. 41. The direct-light-type backlight unit is so constituted that thelight emitted by the cold-cathode tubes 102 a to 102 d therein is,either directly or after having been reflected by the reflector 110,uniformly diffused through the diffuser 130, and then applied to theliquid crystal panel disposed adjacent to the unit.

For any of edge-light-type (sidelight-type) or direct-light-typebacklight units, any of cold-cathode tubes 102, 102 a to 102 d, and 104to 108 of the same type are used. The cold-cathode tube is made of aglass tube 136 with an electrode fixed on both of its sides, and theinner surface of the glass tube 136 is coated with a phosphor 138.Mercury, argon and neon are sealed in the glass tube 136. For the glasstube 136, generally used is hard glass having a refractive index of 1.5or so.

When an electric current is applied between the two electrodes fixed onthe glass tube 136, the mercury gas sealed in the glass tube 136 isexcited, and radiates UV rays (essentially UV rays having a wavelengthof 185 nm or 254 nm). The phosphor 138 coated on the inner surface ofthe glass tube 136 absorbs the UV rays, and emits visible light. Thevisible light is radiated outside the glass tube 136, and is utilizedfor illuminating liquid crystal panels.

Prior Art 4

A conventional cold-cathode tube serving as a light source that receivesessentially the fluorescence of the UV rays having been emitted throughdischarge emission of mercury or the like and emits visible light, forexample, that for a light source for liquid crystal displays and othersis described with reference to FIG. 44A and FIG. 44B. For the lightsource for liquid crystal displays, cold-cathode tubes coated withphosphors capable of emitting light of three primary colors are used.For ordinary cold-cathode tubes, a phosphor mixture prepared by mixing(SrCaBa)₅(PO₄)₃CL:Eu, LaPO₄:Ce,Tb, Y₂O₃:Eu and the like in apredetermined ratio is baked on the inner surface of the glass tube 136,as in FIG. 44A. The phosphors are white translucent powders, and theyare fixed on the inner surface of the cold-cathode tube generally via abinder consisting essentially of water glass. Cold-cathode tubes of thattype, reflectors (essentially made of aluminum) to surround them, and atabular optical waveguide (acrylic plate) are assembled into a backlightunit such as that shown in FIG. 37A and FIG. 37B, and the unit isdisposed behind a liquid crystal panel.

Prior Art 5

A surface light source unit having electric discharge tubes therein isgrouped into two types, one being a direct-light-type unit and the otherbeing a sidelight-type unit, as so mentioned hereinabove. However, thestructures of these types illustrated in FIG. 37A through FIG. 41 andFIG. 43 are problematic in that they could hardly satisfy all therequirements for overall thickness reduction, uniform light diffusionand increased luminance. Specifically, the direct-light-type unit canrealize increased luminance relatively with ease, but could hardlyensure uniform light diffusion owing to the luminance difference betweenthe area around the discharge tubes and the area remote from thedischarge tubes. In addition, since the discharge tubes are disposedbelow the light-emitting member therein, the overall thickness of thedirect-light-type unit is difficult to reduce. Moreover, the positionalrelationship between the discharge tubes and the light curtain disposedbetween the diffuser and the discharge tubes is a matter of greatimportance to the direct-light-type unit, but it is difficult toappropriately align them in every unit. For these reasons,direct-light-type units actually produced on an industrial scale ofteninvolve the problem of luminance fluctuation among them.

On the other hand, the sidelight-type unit can be thinned with ease andcan ensure uniform light diffusion also with ease, but its luminance isdifficult to increase since the incident light utilization in theoptical waveguide therein is low. To solve the problem, Japanese PatentLaid-Open No. 248495/1995 discloses a backlight unit of a different typeas in FIG. 45. As illustrated in FIG. 45, the backlight unit has a UVlamp 300 partly covered with a reflective film 308, and has a dichroicmirror 304 disposed between the UV lamp 300 and an optical waveguide302. In this, the mirror 304 faces the UV lamp 300; and a phosphor film306 is laminated on the mirror 304, and this faces the optical waveguide302. Owing to its wavelength selectivity, the dichroic mirror 304disposed in this unit can pass substantially UV rays only through it,and it greatly improves the luminescent light utilization efficiency ofthe unit.

In the prior art 1, the method of filling the outer peripheral space ofa cold-cathode tube with a liquid of which the refractive index isnearly the same as that of the glass material that forms the outer wallof the cold-cathode tube is problematic in that the light diffusionthrough the optical waveguide is not good. FIG. 39 shows a backlightunit in which the outer peripheral space of each cold-cathode tube isfilled with a liquid, and this is seen in the same direction as that forthe view of FIG. 37B. In FIG. 39, the same constituent members as thosein FIGS. 37A and 37B are designated by the same numeral references astherein. The light source unit (composed of the cold-cathode tubes 102,104 and the reflector 110) is filled with a transparent liquid 116 ofwhich the refractive index is nearly the same as that of the glass tubefor the cold-cathode tubes 102, 104, and is connected with the opticalwaveguide 100 via an optical adhesive 120 therebetween. The same shallapply to the light source unit (composed of the cold-cathode tubes 106,108 and the reflector 112) on the opposite side.

In this structure however, the part extending from the cold-cathodetubes 102, 104 to the optical waveguide 100 form a substantiallycontinuous body. In this part, therefore, the optical waveguide 100 willlose the waveguide condition for it (the condition is that, inprinciple, all the light from the cold-cathode tubes entirely enters theoptical waveguide 100 on its side surface at an incident angle largerthan the critical angle thereto). By way of example, a light source unitof FIG. 40 is referred to. In the case where the optical adhesive 122and the transparent liquid 118 are not present in the unit, for example,the light from the cold-cathode tube 106 shall be refracted at one endof the optical waveguide 100 to run in the refracted direction of thedotted line P. With that, the thus-refracted light will run through theoptical waveguide 100 while undergoing repeated total reflectiontherein. However, in case where the refractive index of the members thatform the optical path is unified by the optical adhesive 122 and thetransparent liquid 118, the light from the cold-cathode tube could notbe refracted but shall go straight ahead as in the solid line Q, and itwill be out of the optical waveguide 100.

Next discussed hereinunder are the problems with the prior art 2 and theprior art 3. The problem with the liquid crystal display panel equippedwith a backlight unit of FIG. 41 is analyzed with reference to the viewof FIG. 42. FIG. 42 shows the right-side light source unit of thestructure of FIG. 41. Of the light having been emitted by thecold-cathode tube 102, the light m1 running toward the optical waveguide100 directly enters the optical waveguide 100 through its end. The lightm2 running toward the reflector 110 opposite to the optical waveguide100 is reflected by the reflector 110, and then enters the opticalwaveguide 100 through its end.

However, the light 3 that is reflected by the reflector 110 and againenters the cold-cathode tube 102, and the light m4 that directly entersthe neighboring cold-cathode tube 104 will be absorbed by the phosphorsexisting in the cold-cathode tubes 102, 104 or will be multi-reflectedin different directions by the glass that forms the cold-cathode tubes,depending on the incident angle of these rays m3 and m4 entering thecold-cathode tubes 102, 104. As a result, some light emitted by thecold-cathode tubes could not enter the optical waveguide 100. Even ifthe light having entered the cold-cathode tubes 102, 104 could be againemitted from them, it will be again reflected by the reflector 110 andwill further again enter the cold-cathode tubes 102, 104, and, afterall, the light will be significantly attenuated. For these reasons, thelight emitted by the cold-cathode tubes 102, 104 could not beefficiently utilized in the unit, thereby causing the problem of thereduction in light emission efficiency of the unit and the problem ofthe insufficiency of luminescent light quantity in the unit.

To increase the light quantity in the unit, increasing the number ofcold-cathode tubes therein and increasing the electric power to beapplied to the cold-cathode tubes may be taken into consideration,which, however, will produce still other problems. Increasing the numberof cold-cathode tubes will inevitably enlarge the overall size of thelighting unit; and increasing the electric power to be applied to thecold-cathode tubes will increase the quantity of heat to be generated bythe light source and will increase the light emission noise of thecold-cathode tubes.

Japanese Utility Model Laid-Open No. 59402/1993 and Japanese Patent No.2,874,418 have proposed a technique of optimizing the shape ofreflectors for direct-light-type backlight units. In direct-light-typebacklight units, however, the reflector must produce uniformly reflectedrays that are parallel with each other. Therefore, the proposedtechnique is problematic in that that the intended optimization islimited as it must satisfy the requirement as above and must increasethe reflector efficiency. As opposed to the direct-light-type backlightunits, sidelight-type backlight units could easily solve the problemsince the light emitted by the cold-cathode tubes therein may bedirectly led into the optical waveguide. However, owing to thelimitation on the thickness of the lighting unit, the diameter of eachcold-cathode tube must be at most 3 mm, preferably 2.6 mm or so,relative to the aperture of the reflector (in general, it is at most 10mm and is preferably 8 mm or so). Therefore, the method of increasingthe number of cold-cathode tubes in sidelight-type backlight units islimited, and increasing the luminance of the units is thereforedifficult.

In addition, the above-mentioned prior art techniques involve stillanother problem in that the luminous efficiency (light emissionefficiency) of the cold-cathode tubes employed therein is only 30lumens/W of the inputted power, and is extremely small.

Next discussed is the problem with the prior art 4. In the structure ofFIG. 44A, the emission efficiency will lower when the visible light isemitted out of the cold-cathode tube. The reason is because a gaseous(or vacuum) space 202 is formed between the powdery phosphor particles200 and the glass tube 136, as in FIG. 44B. When the visible raysemitted on the surfaces of the phosphor particles have reached the glasstube 136, some of them are reflected on the surface of the glass tubelike X1, while some others pass through the glass tube like X2. Sincethe glass material to form the cold-cathode tube generally has arefractive index of 1.48 or so, the surface reflection X1 causes areflection loss of around 10%.

In this connection, analyzed is a case where some external visible lightenters the cold-cathode tube, with reference to FIG. 44B. When light(designated by solid lines in FIG. 44B) enters the glass tube 136through its outer surface (this is on the lower side in FIG. 44B), theincident light is reflected on the surfaces of the phosphor particles200 that are in contact with the space 202. In this case, however, sincethe surfaces of the particles are not smooth and since the diameterthereof is 3 μm or so and is small, the reflected light shall bemacroscopically considered as scattered light. Therefore, the lightpassing through the cold-cathode tube or reflected by the phosphorparticles will lose its running orientation, and will be therebydiffused and reflected as in the manner designated by the dotted linesin FIG. 44B. As a result, in the lighting unit with conventionalcold-cathode tubes therein, the light having entered the cold-cathodetubes shall be lost. The light loss increases to a higher degree in moresmall-sized lighting units. In current backlight units, about 60% of theoverall light emission will re-enter the cold-cathode tubes, and 30% ofthe light having re-entered them (this corresponds to about 18% of theoverall light emission) will be scattered or absorbed by the phosphorsand will be thereby lost.

Next discussed is the problem with the prior art 5. Even in thestructure of FIG. 45, a part of UV rays having been emitted by the UVlamp 300 will be multi-reflected in different directions in the UV lamp300 and will be absorbed by the gas existing therein. Therefore, theproblem with the structure is that the quantity of UV rays to be emittedoutside by the UV lamp decreases and the emission efficiency of thestructure could not be increased. In addition, when the gas in the UVlamp absorbs too much light, the temperature of the UV lamp rises.Therefore, the size of the UV lamp could not be reduced. Another problemwith the structure is that the light loss therein is great since thelight emitted by the UV lamp is scattered in the UV lamp and is absorbedby the gas existing therein.

In the sidelight-type backlight unit, optical elements that may disorderthe waveguide condition, such as the diffusive surface of the diffuser130 and the refractive and reflective surface of the reflector 132, maybe disposed in any desired density, whereby the quantity distribution ofthe light that passes through the optical waveguide 100 can becontrolled, and the backlight unit ensures illumination of extremelyhigh uniformity. In addition, the backlight unit of the type ischaracterized in that even when some of the light-emitting surfaces ofthe cold-cathode tubes 102 to 108 are aged so that the light emissionthrough them is lowered, the unit could seemingly emit uniform lightsince the distance between the cold-cathode tubes and the panel surfaceto be illuminated by the unit is long. On the contrary, however, sincethe cold-cathode tubes 102 to 108 are disposed adjacent to the sideedges of the optical waveguide 100 in the backlight unit of the type,the number of the cold-cathode tubes that may be in the unit is limited.Therefore, one problem with the unit of the type is that it is difficultto increase the luminance of the unit.

On the other hand, the direct-light-type sidelight unit is advantageousin that its luminance can be increased by increasing the number of thecold-cathode tubes 102 a to 102 d, but is problematic in that itsluminance is often uneven since the distance between the cold-cathodetubes 102 a to 102 d and the panel surface to be illuminated by the unitis not long. It may be possible to optimize the distance between thecold-cathode tubes 102 a to 102 d, the characteristics of the diffuser130 and the profile of the reflector 110 to thereby evade luminancefluctuation. However, when the conditions are varied, some of thelight-emitting surfaces of the cold-cathode tubes 102 a to 102 d will beaged to lower the light emission through them, and one problem with theunit of the type is that its luminance will readily fluctuate.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a backlight unit inwhich the light emitted by the cold-cathode tubes can be efficientlyreflected toward the optical waveguide.

The object of the invention is to provide a long-life lighting unitcapable of realizing high luminance of high uniformity.

The object can be attained by a lighting unit which comprises an emitterhaving a transparent body with a refractive index n0 and containing alight-emitting substance sealed in the empty region inside it, a housingthat houses the emitter and has a reflector formed on its inner surface,a transparent filler with a refractive index n1 filled in the housing,and an optical waveguide made of a transparent substance with arefractive index n2 and having a light-emitting surface; wherein theprofile of the light-reflecting surface of the reflector is so modifiedthat the light having been emitted by the emitter and reflected by thereflector to run toward the light-emitting surface of the opticalwaveguide can reach the light-emitting surface at an incident angle notsmaller than the critical angle to the light-emitting surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A and FIG. 1B show an outline of the constitution of the backlightunit of Example 1 of the first embodiment of the invention;

FIG. 2 shows a part of the constitution of the backlight unit of Example2 of the first embodiment of the invention;

FIG. 3 shows a part of the constitution of the backlight unit of Example3 of the first embodiment of the invention;

FIG. 4A to FIG. 4C show an outline of the constitution of the backlightunit of Example 4 of the first embodiment of the invention;

FIG. 5 shows an outline of the constitution of the backlight unit ofExample 6 of the first embodiment of the invention;

FIG. 6 shows an outline of the constitution of the backlight unit ofExample 1 of the second embodiment of the invention;

FIG. 7 shows an outline of the constitution of the backlight unit ofExample 2 of the second embodiment of the invention;

FIG. 8 shows an outline of the constitution of the backlight unit ofExample 3 of the second embodiment of the invention:

FIG. 9 shows an outline of the constitution of the backlight unit ofExample 1 of the third embodiment of the invention;

FIG. 10 shows an outline of the constitution of the backlight unit ofExample 2 of the third embodiment of the invention;

FIG. 11A and FIG. 11B show an outline of the constitution of thebacklight unit of Example 3 of the third embodiment of the invention;

FIG. 12 shows an outline of the constitution of the backlight unit ofExample 4 of the third embodiment of the invention;

FIG. 13 shows an outline of the constitution of the backlight unit ofModification 1 of Example 4 of the third embodiment of the invention;

FIG. 14 shows an outline of the constitution of the backlight unit ofModification 2 of Example 4 of the third embodiment of the invention;

FIG. 15 shows an outline of the constitution of the backlight unit ofExample 5 of the third embodiment of the invention;

FIG. 16 shows an outline of the constitution of the backlight unit ofExample 6 of the third embodiment of the invention;

FIG. 17 shows an outline of the constitution of the backlight unit ofExample 7 of the third embodiment of the invention;

FIG. 18 is to explain the effect of Example 7 of the third embodiment ofthe invention;

FIG. 19 shows an outline of the constitution of the backlight unit ofExample 8 of the third embodiment of the invention;

FIG. 20 shows an outline of the constitution of the backlight unit ofExample 9 of the third embodiment of the invention;

FIG. 21 shows an outline of the constitution of the backlight unit ofExample 10 of the third embodiment of the invention;

FIG. 22A to FIG. 22C show an outline of the constitution of the lightsource of Example 1 of the fourth embodiment of the invention;

FIG. 23A and FIG. 23B show an outline of the constitution of the lightsource of Example 2 of the fourth embodiment of the invention;

FIG. 24A and FIG. 24B show an outline of the constitution of the lightsource of Example 3 of the fourth embodiment of the invention;

FIG. 25 is a graph showing the metal concentration in Example 3 of thefourth embodiment of the invention;

FIG. 26A and FIG. 26B show an outline of the constitution of the lightsource of Example 4 of the fourth embodiment of the invention;

FIG. 27 shows an outline of the constitution of the light source unit ofExample 1 of the fifth embodiment of the invention;

FIG. 28 shows an outline of the constitution of the light source unit ofExample 2 of the fifth embodiment of the invention;

FIG. 29A to FIG. 29C show an outline of the constitution of the lightsource unit of Example 3 of the fifth embodiment of the invention;

FIG. 30A and FIG. 30B show an outline of the constitution of the lightsource unit of Example 4 of the fifth embodiment of the invention;

FIG. 31 shows an outline of the constitution of the light source unit ofExample 5 of the fifth embodiment of the invention;

FIG. 32A and FIG. 32B show an outline of the constitution of the lightsource unit of Example 6 of the fifth embodiment of the invention;

FIG. 33A and FIG. 33B show an outline of the constitution of thebacklight unit and the liquid crystal display of Example 7 of the fifthembodiment of the invention;

FIG. 34 shows an outline of the constitution of the backlight unit andthe liquid crystal display of Example 8 of the fifth embodiment of theinvention;

FIG. 35A to FIG. 35D show an outline of the constitution of the lightsource unit of Example 9 of the fifth embodiment of the invention;

FIG. 36 shows an outline of the constitution of the light source unit ofExample 10 of the fifth embodiment of the invention;

FIG. 37A and FIG. 37B show an outline of the constitution of aconventional backlight unit;

FIG. 38 is to explain the problem with the conventional backlight unit;

FIG. 39 shows an outline of the constitution of a conventional backlightunit;

FIG. 40 is to explain the problem with the conventional backlight unit;

FIG. 41 shows an outline of the constitution of a conventional backlightunit;

FIG. 42 is to explain the problem with the conventional backlight unit;

FIG. 43 shows an outline of the constitution of a conventional backlightunit;

FIG. 44A and FIG. 44B are to explain the problem with the conventionalbacklight unit;

FIG. 45 shows an outline of the constitution of a conventional backlightunit;

FIG. 46 shows an outline of the basic constitution of the lighting unitof the sixth embodiment of the invention, illustrating thecross-sectional view of the lighting unit disposed adjacent to thesurface of the liquid crystal panel FP to be illuminated by it;

FIG. 47 shows an outline of the lighting unit of Example 6-1 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 48 shows an outline of the lighting unit of Example 6-2 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 49 shows an outline of the lighting unit of Example 6-3 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 50 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of Example 6-3 of the sixth embodiment of theinvention;

FIG. 51 is a partly enlarged view around the cold-cathode tube 402 c ina modification of the lighting unit of Example 6-3 of the sixthembodiment of the invention;

FIG. 52 is a partly enlarged view around the cold-cathode tube 402 c inanother modification of the lighting unit of Example 6-3 of the sixthembodiment of the invention;

FIG. 53 shows an outline of the lighting unit of Example 6-4 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 54 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of Example 6-4 of the sixth embodiment of theinvention;

FIG. 55 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of Example 6-4 of the sixth embodiment of theinvention;

FIG. 56 shows an outline of a modification of the lighting unit ofExample 6-4 of the sixth embodiment of the invention, illustrating thecross-sectional view of the modified lighting unit disposed adjacent tothe surface of the liquid crystal panel FP to be illuminated by it;

FIG. 57 shows an outline of the lighting unit of Example 6-5 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 58 shows an outline of the lighting unit of Example 6-6 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 59 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of Example 6-6 of the sixth embodiment of theinvention;

FIG. 60 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of Example 6-6 of the sixth embodiment of theinvention;

FIG. 61 shows an outline of a modification of the lighting unit ofExample 6-6 of the sixth embodiment of the invention, illustrating thecross-sectional view of the modified lighting unit disposed adjacent tothe surface of the liquid crystal panel FP to be illuminated by it;

FIG. 62 shows an outline of another modification of the lighting unit ofExample 6-6 of the sixth embodiment of the invention, illustrating thecross-sectional view of the modified lighting unit disposed adjacent tothe surface of the liquid crystal panel FP to be illuminated by it;

FIG. 63 is a partly enlarged view around the cold-cathode tube 402 c inthe lighting unit of FIG. 62;

FIG. 64 is a partly enlarged view around the cold-cathode tube 402 c instill another modification of the lighting unit of Example 6-6 of thesixth embodiment of the invention;

FIG. 65 shows an outline of the lighting unit of Example 6-7 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 66A and FIG. 66B are views showing different light diffusions inthe lighting unit 401 of Example 6-7 of the sixth embodiment of theinvention, concretely explaining the difference in the emitted lightdiffusion between the case having a diffusion pattern 410 (FIG. 66A) andthe case having triangular recesses 426 (FIG. 66B);

FIG. 67 shows an outline of the lighting unit of Example 6-8 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 68 shows an outline of the lighting unit of Example 6-9 of thesixth embodiment of the invention, illustrating the cross-sectional viewof the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 69 shows an outline of the lighting unit of Example 7-1 of theseventh embodiment of the invention, illustrating the cross-sectionalview of the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 70 is a view to show the illumination mode of the lighting unit ofExample 7-1 of the seventh embodiment of the invention;

FIG. 71 shows an outline of the lighting unit of Example 7-2 of theseventh embodiment of the invention, illustrating the cross-sectionalview of the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 72 is a view to show the illumination mode of the lighting unit ofExample 7-2 of the seventh embodiment of the invention;

FIG. 73 shows an outline of the lighting unit of Example 7-3 of theseventh embodiment of the invention, illustrating the cross-sectionalview of the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 74 shows an outline of the lighting unit of Example 7-4 of theseventh embodiment of the invention, illustrating the cross-sectionalview of the lighting unit disposed adjacent to the surface of the liquidcrystal panel FP to be illuminated by it;

FIG. 75 shows an outline of a modification of the lighting unit ofExample 7-4 of the seventh embodiment of the invention, illustrating thecross-sectional view of the modified lighting unit disposed adjacent tothe surface of the liquid crystal panel FP to be illuminated by it;

FIG. 76A, FIG. 76B and FIG. 76C show an outline of the lighting unit ofExample 7-5 of the seventh embodiment of the invention, illustrating theplan view and the cross-sectional views of the lighting unit disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it;

FIG. 77A, FIG. 77B and FIG. 77C show an outline of a modification of thelighting unit of Example 7-5 of the seventh embodiment of the invention,illustrating the plan view and the cross-sectional views of the modifiedlighting unit disposed adjacent to the surface of the liquid crystalpanel FP to be illuminated by it;

FIG. 78 is an enlarged view showing a part of the cross section aroundthe wall of a conventional cold-cathode tube cut in the direction alongwith the axial direction of the tube;

FIG. 79 is a cross-sectional view of the cold-cathode tube of Example8-1 of the eighth embodiment of the invention, cut in the directionperpendicular to the axial direction of the tube;

FIG. 80 is an enlarged view showing a part of the cross section aroundthe wall of the cold-cathode tube of Example 8-1 of the eighthembodiment of the invention, cut in the direction along with the axialdirection of the tube;

FIG. 81 is a cross-sectional view of the visible light source 470 ofExample 8-2 of the eighth embodiment of the invention, cut in thedirection perpendicular to the axial direction of the UV source;

FIG. 82 is an enlarged view showing the details of the constitution ofthe emission filter 476 disposed adjacent to the visible light source470 of Example 8-2 of the eighth embodiment of the invention;

FIG. 83 is a cross-sectional view of the visible light source of Example8-3 of the eighth embodiment of the invention, cut in the directionperpendicular to the axial direction of the UV source;

FIG. 84 is an enlarged view showing the details around the phosphorlayer 494 attached to the aluminum mirror 492 in Example 8-3 of theeighth embodiment of the invention; and

FIG. 85 is an enlarged view showing the details around the phosphorlayer 494 attached to the mercury discharge tube 490 in Example 8-3 ofthe eighth embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The backlight unit for liquid crystal displays and others of the firstembodiment of the invention is described with reference to FIG. 1Athrough FIG. 5. This embodiment provides a backlight unit in which theemitted light is prevented from leaking out of the optical waveguide notundergoing total reflection, even when the light source unit therein isso constituted that the outer peripheral region of each cold-cathodetube therein is filled with a liquid of which the refractive index n1 isnearly the same as the refractive index n0 of the glass material thatforms the outer wall of the cold-cathode tube.

In order that a majority of the emitted light can run through theoptical waveguide, some methods mentioned below maybe employed. Thefirst method comprises changing the angle of the emitted light in theprevious stage before the light enters the optical waveguide so that thelight is specifically oriented in the direction falling within the anglerange that meets the optical waveguide condition. For example, thelight-reflecting surface of the reflector adjacent to the opticalwaveguide in the light source unit is curved convexedly toward thecold-cathode tubes therein so that the incident angle of the raycomponent that reaches the side surface of the optical waveguide at alarge incident angle is changed.

The second method comprises reducing the degree of light emission fromthe region of the light-emitting surface of the optical waveguide nearerto the cold-cathode tubes. For example, a reflection pattern is providedon the surface of the optical waveguide, and the a real ratio of theopenings of the pattern is distributed depending on the light quantitydistribution on the pattern.

The other methods are as follows: For example, the dielectric losstangent of the transparent liquid is made to decrease under the drivingcondition for the cold-cathode tubes. The dielectric constant of thetransparent liquid is made to increase under the driving condition forthe cold-cathode tubes. A cooling mechanism is provided in a part of thehousing of the light source unit. A radiation fin is provided partlyaround the housing. The refractive index of the liquid to be filled inthe light source unit is controlled to thereby prevent the reduction inthe emission efficiency caused by reflection. The reflector existing ina part of the housing is made of metal. A means for heating thetransparent liquid filled in the light source unit is provided. Amechanism is provided for heating the transparent liquid for apredetermined period of time after lighting.

The backlight unit of this embodiment is described with reference to itsconcrete examples. In the other embodiments of the invention and theirexamples to be mentioned hereinunder, the constituent elements havingthe same effect and the same function among them, and the constituentelements having the same effect and the same function as those in theprior art techniques mentioned above will be designated by the samenumeral references, and repeatedly describing them is omittedhereinunder.

Example 1 of the First Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 1A and FIG. 1B. Like FIG. 37B, FIG. 1Aand FIG. 1B are cross-sectional views of a backlight unit, especiallyclarifying the region around the light source unit of the backlightunit. FIG. 1A shows the driving principle of the backlight unit; andFIG. 1B shows the constitution thereof. The backlight unit in liquidcrystal monitors (televisions) is provided with a prism sheet, adiffuser and other members between the unit and the liquid crystal paneladjacent thereto. However, such members have no specific relation tothis embodiment of the invention, and their description is omittedherein. In the backlight unit, especially the cold-cathode tubes, thereflector and the optical waveguide are specifically described.

In order that the emitted light from the light source unit thatcomprises at least the housing 6, the cold-cathode tubes 2, 4, and thetransparent liquid 8 can be properly guided by the optical waveguide 1to pass through it, the incident angle of the emitted light to the sidesurface S (or S′) of the optical waveguide 1 must be at least thecritical angle thereto, as in FIG. 1A and FIG. 1B. For this Example, theprofile of the light-reflecting surface of the reflector 10 that formsthe inner surface of the housing 6 of the light source unit is modifiedto thereby control the going-out angle of the emitted light from thelight-reflecting surface. In this Example, two cold-cathode tubes 2, 4each having an outer diameter of 2.6 mm are packaged in the light sourceunit. The reflector 10 has a nearly rectangular cross-sectional profileformed by connecting the edges T-U-V-W, and this covers the cold-cathodetubes 2,4 while being spaced by a minimum distance 1 mm from the tubes2,4, as in FIG. 1A.

The profile of the reflector 10 that connects T-X shall be determined inthe manner mentioned below. The profile of W-Y is symmetric to that ofT-X. The optical path of the light that goes out of the inner surfacesof the two cold-cathode tubes 2, 4 (these surfaces are coated with aphosphor) and is reflected on the surface of T-X to reach the surface S(S′) is discussed. First, a tangential line 11 is drawn. This startsfrom a position between T-X, for example, from the position a in FIG.1A, and tangentially extends to the inner surface of the cold-cathodetube 4. Next, a virtual straight line 11′ is drawn. This starts from theposition α and reaches the surface S (or S′), and its incident angle tothe surface is the critical angle thereto (for example, 42°). The degreeof inclination of the surface of the reflector 10 at the position α isso determined that the bisector of the angle between the tangential line11 and the virtual straight line 11′ is a normal line. This operation isrepeated in order from T to X to finally determine the profile of thecurved surface T-X.

In the manner as above, the backlight unit of this Example comprises thecold-cathode tubes (emitters) 2, 4 both having a glass tube (transparentbody with a refractive index n0) with a light-emitting substance beingsealed in the empty region inside it; the housing 6 that houses thecold-cathode tubes 2, 4 and has the reflector 10 formed on its innersurface; the transparent liquid (filler) 8 with a refractive index n1(≈n0) filled in the housing 6; and the optical waveguide 1 made of atransparent substance with a refractive index n2 and having alight-emitting surface, and this is characterized in that the profile ofthe light-reflecting surface of the reflector 10 is so modified that thelight having been emitted by the emitter and reflected by the reflector10 to run toward the light-emitting surface S of the optical waveguide 1can reach the light-emitting surface S at an incident angle not smallerthan the critical angle to the light-emitting surface S.

The profile of the light-reflecting surface of the reflector 10 ischaracterized in that it satisfies the requirement of|θ1−θ2|<cos⁻¹(1/n2), in which θ1 indicates the angle between the normalline n at a position α on the surface and the tangential line 1 thattangentially connects the point of the position α and the outline of theempty region, and θ2 indicates the angle between the line segment m thatis parallel to the light-emitting surface S (S′) and is in the planeformed by the normal line n and the tangential line 1, and the normalline n.

When the incident angle of the light that reaches the light-emittingsurface S (S′) is designated by θ3 and when the light undergoes totalreflection on the surface, then n2 sin θ3>1 according to the Snell'slaw. From FIG. 1A, θ3+θ4=π/2, n2 sin θ4>1, and θ4=θ1−θ2|. Therefore, n2cos(|θ1−θ2|)>1, and the above-mentioned formula is derived from this.

In the manner as above, when the bell-shaped reflector 10 of which thelight-reflecting surface is curved convexedly toward the cold-cathodetubes cold-cathode tubes 2, 4 is disposed between X-T and Y-W, the lightcomponent that may pass through the surfaces S, S′, not undergoing totalreflection thereon, can be reduced.

As in FIG. 1B, the region between X-Y is sealed up with a transparentacrylic sheet 12, and the closed space formed by the reflector 10,X-T-U-V-W-Y, and the transparent acrylic sheet 12, X-Y, is filled withsilicone oil 8. The optical and electric characteristics of the siliconeoil 8 are shown in Table 1.

TABLE 1 Characteristic of Silicone Oil Refractive Index 1.486 DielectricConstant 3 × 10⁻⁴ (10² Hz), 3 × 10⁻⁴ (10⁶ Hz) Dielectric Loss Tangent2.9 × 10⁻³ (10² Hz), 2.8 × 10⁻³ (10⁶ Hz) Volume Resistivity 1 × 10¹⁴ Ω ·m

As in Table 1, when the silicone oil 8 is so selected that itsrefractive index falls between the refractive index (1.48) of theacrylic resin that forms the optical waveguide 1 and the refractiveindex (1.49) of the glass material that forms the cold-cathode tubes 2,4, then the interfacial reflectivity can be minimized. In addition, whenthe electric characteristics of the thus-selected silicone oil 8 areoptimized, then the leak current to the reflector 10 (formed ofaluminum) can be reduced. Regarding the direct current component, theelectric energy loss in its leakage can be reduced when the dielectricloss tangent of the silicone oil 8 is controlled to be on the order of10⁻³. Regarding the alternating current component, the capacitancebetween the cold-cathode tubes 2, 4 and the reflector 10 can beincreased when the silicone oil 8 is so selected that its dielectricconstant is the highest at a frequency of around 400 Hz, and thereforethe leakage of the component can be reduced in that condition.

The housing 6, X-T-U-V-W-Y, is connected with the optical waveguide 1via a support ring 16 with an optical adhesive 14 being appliedtherebetween. A radiation fin 35 is provided adjacent to the outersurface of the housing 6. The heat generated by the cold-cathode tubes2, 4 is conducted by the housing 6 and then radiated outside by theradiation fin 35, and the light source unit is thereby cooled.

Example 2 of the First Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 2. Additionally having a forcedair-cooling mechanism, this Example is a modification of Example 1.Precisely, an axial fan 18 having a square size of 20 mm×20 mm isprovided behind the reflector 10 of a metal plate (e.g., aluminum plate)that forms the housing 6, and this applies flowing air onto the outersurface of the reflector 10. The axial fan 18 is provided with arevolution speed control mechanism 22. Based on the temperature of thetransparent liquid 8, the revolution speed control mechanism 22 controlsthe revolution speed of the axial fan 18. The temperature of thetransparent liquid 8 is monitored, for example, on the basis of thethermo-electromotive force difference between the cromel 20 embedded ina part of the reflector 10 and the aluminum material that forms thereflector 10. With the mechanism, the liquid temperature can be loweredby 10° C or so.

Example 3 of the First Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 3. Additionally having a mechanism forheating the transparent liquid 8, this Example is another modificationof Example 1. In case where the transparent liquid 8 is not heated, itwill be about 15 minutes before the light source unit reaches thermalequilibrium. In addition, since the initial-stage temperature of theunit is lower by about 20° C. than the thermal equilibrium temperaturethereof, the mercury vapor pressure inside the cold-cathode tubes 2, 4could not well increase. In the initial stage, therefore, the luminanceof the cold-cathode tubes 2, 4 will be about 60% of the ordinaryluminance thereof driven for a while. To solve the problem of lowluminance condition in rise time, the backlight unit of this Example isprovided with a mechanism for heating the transparent liquid 8 for about10 minutes or so after the cold-cathode tubes 2, 4 have been turned on.

As in FIG. 3, the cold-cathode tubes 2, 4 are connected with an inverterpower source 28 that powers them. When the switch 30 is turned on(on-switch), DC 12V is supplied to the inverter power source 28. Inaddition, when the switch 30 is turned on, the timer 26 is therebydriven. The timer 26 thus driven in the on-switch condition startscount-down, and the ribbon heater 24 is then switched on.

The ribbon heater 24 is disposed in contact with the transparent liquid8 in the light source unit of FIG. 1A through FIG. 2, and after havingbeen electrified, this generates heat to warm up the transparent liquid8. The timer 26 controls the current supply to the ribbon heater 24 sothat the ribbon heater 24 is switched off after a predetermined periodof time, for example, after 10 minutes. With that, the light source unitcan reach the thermal equilibrium condition as soon as possible, and itsproblem of low-luminance condition can be solved within a short periodof time.

In the above-mentioned Examples, employed is the first method of makingit possible to orient the emitted light so that the majority of theemitted light can be reflected on the light-emitting surface of theoptical waveguide. In other words, the method employed in these examplescomprises changing the angle of the emitted light in the previous stagebefore the light enters the optical waveguide so that the light isspecifically oriented in the direction falling within the angle rangethat meets the optical waveguide condition. Being different from this,the second method is employed in the following Example 4, which is forreducing the degree of light emission from the region of thelight-emitting surface of the optical waveguide nearer to thecold-cathode tubes.

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 4A to FIG. 4C. FIG. 4A is a view of thebacklight unit of this Example seen on its emission side. FIG. 4B is across-sectional view of FIG. 4A cut along the line A—A. As illustrated,the backlight unit comprises an acrylic plate 1 (this serves as anoptical waveguide) with a light-scattering pattern 114 formed on itsback surface, and two cold-cathode tubes 2, 4 disposed nearly inparallel with each other on and along one side of the acrylic plate 1. Ahousing 6 having a reflector 10 (for this, an aluminum film is popularlyused) on its inner surface is provided to surround the two cold-cathodetubes 2, 4, and its one side is opened to the optical waveguide 1 facingthereto.

Also on and along the other side of the optical waveguide 1 having thetwo cold-cathode tubes 2, 4 disposed on its one side, other twocold-cathode tubes 2, 4 are disposed nearly in parallel with each other,and a housing 6 having reflector 10 on its inner surface is provided tosurround the two cold-cathode tubes 2, 4 with its one side being openedto the optical waveguide 1 facing thereto. The reflector 10 of thehousing 6 in this Example is formed to have a rectangularcross-sectional profile, which is not convexedly curved and is differentfrom that in Example 1. In this Example, the cold-cathode tubes 2,4(these maybe the same as in Example 1) are so spaced from each otherthat the narrowest distance between them is 1 mm.

The open end of each housing 6 is sealed up with an acrylic sheet (notshown) by the use of a silicone sealant applied therebetween. Thehousings 6 are filled with a silicone-type transparent liquid 8, like inExample 1. The housings 6 are fixed to the optical waveguide with anoptical adhesive 14 applied therebetween, with the acrylic sheet of eachhousing 6 facing the opposite sides of the optical waveguide 1.

The optical waveguide 1 is made of an acrylic plate having, for example,a size of 300 (mm)×400 (mm)×8 (mm) or so. Its surface seen on FIG. 4A isthe light-emitting surface, and this is disposed adjacent to a liquidcrystal panel. The light-scattering pattern 114 to be provided on thesurface of the optical waveguide 1 opposite to the light-emittingsurface thereof is formed by uniformly printing thereon dots of a whitelight-scattering substance having a diameter of 2 mm or so. The dotpattern acts to scatter the light that runs through the opticalwaveguide 1, and the thus-scattered light is emitted through thelight-emitting surface of the optical waveguide 1.

On the light-emitting surface, provided are a plurality of reflectivesilver dots 32. The reflective dots 32 are provided so as to make thelight that will directly pass through the light-emitting surface of theoptical waveguide 1, which is not undergoing total reflection, go backinto the optical waveguide 1. The ratio of the nude region not coatedwith the reflective dots 32 shall be determined in the manner mentionedbelow.

The angle distribution of the light that goes out through one point ofthe cold-cathode tubes 2, 4, is nearly constant. Therefore, theluminance on the light-emitting surface of the optical waveguide 1 isproportional to the perspective angle at which each of the cold-cathodetubes 2, 4 targets the unit area of the light-emitting surface.Accordingly, if the light-emitting surface undergoes no treatment, theluminance of its region nearer to the cold-cathode tubes will beextremely high. The perspective angle is represented by the followingformula:

δ/δl(tan⁻¹((d/2)/l))=(d×½)/(1² +d ²/4)

wherein d indicates the thickness of the optical waveguide 1; and lindicates the distance from the cold-cathode tubes 2, 4.

To correct the luminance distribution, the reflective dots 32 may be soprovided that the ratio of the dot-free nude region is proportional tothe reciprocal of the luminance distribution. Concretely, the pattern ofthe reflective dots 32 is so designed that the area of the region withno reflective dots 32 provided thereon is proportional to(1²+d²/4)/(d½).

The nude region distribution based on the reflective dots 32 formed inaccordance with the above-mentioned formula may be as in FIG. 4C, incase where the thickness of the optical waveguide 1 is 8 mm and thelength of the side not facing the cold-cathode tubes 2, 4 is 350 mm. InFIG. 4C, the horizontal axis indicates the ratio of the nude region (%);and the vertical axis indicates the distance from the lower end of theoptical waveguide 1 shown in FIG. 4A. When the reflective dots 32 are sopatterned that the ratio of the nude region in the center part of thelight-emitting surface may be 65% or so and the ratio of the nude regionat the both edges of the light-emitting surface may be 11% or so, as inFIG. 4C, then the luminance distribution of the so-designed opticalwaveguide may be unified as compared with the optical waveguide providedwith only the light-scattering pattern 114, as in Table 2.

With the dot pattern of the reflective dots 32, the ratio of the nuderegion of the light-emitting surface of the optical waveguide 1increases monotonously relative to the distance from the cold-cathodetubes 2, 4. Preferably, the ratio of the nude region around the centerpart of the optical waveguide 1 falls between 60 and 75% or so, and theratio of the nude region around the ends thereof adjacent to thecold-cathode tubes 2, 4 falls between 10 and 20% or so.

TABLE 2 Luminance Distribution on Modified or Non-modified OpticalWaveguide (unit: Cd/m²) Luminance (in the center) part of opticalLuminance (1 = 10 mm) waveguide; 1 = 150 mm) Light-scattering 4000 1200pattern only Reflective pattern 1800 1900 added

Example 5 of the First Embodiment

A modification of Example 4 is described. In the backlight unit shown inFIG. 4A through FIG. 4C, the light source unit is disposed adjacent tothe both ends of the optical waveguide 1. In this, the distance betweenthe two light source units, or that is, the length of the opticalwaveguide is represented by w; and the width of the open end of thehousing 6 of each light source unit, or that is, the thickness of theoptical waveguide 1 is represented by d.

In this, w and d are so controlled that they satisfy the requirement of20×d<w<45×d.

This defines the relation between the length of the optical path of theoptical waveguide 1 sandwiched between the two light source units andthe width of the light-emitting surface thereof. The reason why thedistance w between the two light source units must be larger than 20×dis for unifying as much as possible the angle characteristics of theemitted light. If the distance w is not larger than 20×d, the frequencyof light reflection inside the optical waveguide 1 before the lighthaving entered the optical waveguide 1 goes outside it decreases,whereby the optical path through the optical waveguide 1 will be locallyshifted.

On the other hand, the reason why the distance w must be smaller than45×d is for reducing as much as possible the energy loss owing to thelight absorption by the light-scattering pattern 114 or the likeprovided on the light-emitting surface S′ (this may be referred to asthe back surface) of the optical waveguide 1. One reflection on thelight-scattering pattern 114 or the like involves light absorption of atleast 2%. Therefore, the optical waveguide 1 is so designed relative tothe light source units combined with it that the energy loss owing tothe light absorption in the optical path from one end to the other endof the optical waveguide 1 is at most about 25%. When the distance w isequal to 45×d, the frequency of light reflection inside the opticalwaveguide 1 from its one end to the other end may be 13 times onaverage. The energy E to be lost in 13 reflections isE=(1−(0.98)¹³)=0.23, and the energy loss can be lower than the setpoint.

Example 6 of the First Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 5. FIG. 5 is a partly-cutcross-sectional view of a backlight unit seen in the same direction asthat for FIG. 4B. In FIG. 5, the same structural members as those inFIGS. 4A through 4C are designated by the same numeral references, andtheir description is omitted herein.

The light that reaches the side surface of the optical waveguide 1 at asmall incident angle thereto is one that has passed through the regionnear to the reflective surface of the reflector 10 adjacent to thelight-emitting surface S (S′) of the optical waveguide 1 and near to thecold-cathode tubes 2, 4. By the use of an optical path-changing device34, the light passing through this region is refracted by about 10°toward the optical waveguide 1 so as to reduce the incident angle of thethus-refracted light to the optical waveguide 1, thereby improving thelight emission distribution in the optical waveguide 1. For the opticalpath-changing device 34, usable is a hollow prism of acrylic resin. Theoptical path-changing device 34 may be disposed in the transparentliquid 8 at the position at which a part of the light emitted by thecold-cathode tubes 2, 4 will vertically reach the reflective surface ofthe reflector 10 that is on the extended line from the light-emittingsurface S (S′) of the optical waveguide 1.

In the Examples mentioned above, a liquid is filled in the space betweenthe cold-cathode tubes 2, 4 and the reflector 10. The substance to befilled therein may also be putty, adhesive or the like. Needless-to-say,a majority of the space between the cold-cathode tubes 2, 4 and thereflector 10 may be filled with a transparent solid such as an acrylicplate or the like, and the space still remaining between thecold-cathode tubes 2, 4 and the acrylic plate may be filled up with anoptical oil (or an optical adhesive). In short, the filling substanceshall satisfy the two requirements that “it is transparent” and “itsrefractive index is nearly the same as that of the glass to form thecold-cathode tubes and that of the optical waveguide”.

Next described is the backlight unit for liquid crystal displays andothers of the second embodiment of the invention with reference to FIG.6 through FIG. 8. This embodiment is to provide a sidelight-typebacklight unit in which the light from the cold-cathode tubes can beefficiently reflected toward the optical waveguide.

The backlight unit of this embodiment is characterized in that thereflective surface of the reflector which is disposed opposite to theoptical waveguide relative to the cold-cathode tubes and which reflectsthe light having been emitted toward it from the cold-cathode tubes isso specifically designed that a majority of the light reflected thereoncan run toward the space between the cold-cathode tubes adjacent to eachother or toward the space between the cold-cathode tubes and thereflector.

In this embodiment, the light emitted by the cold-cathode tubes towardthe reflector is, after having been reflected by the reflector,prevented from re-entering the cold-cathode tubes but passes through thespace between the cold-cathode tubes adjacent to each other or throughthe space between the cold-cathode tubes and the reflector to safelyreach the optical waveguide, being different from the rays m3, m4 as inFIG. 42 showing a conventional example. Therefore, the backlight unit ofthis embodiment is free from light scattering and absorption owing tothe re-entrance of the reflected light into the cold-cathode tubes andfrom multiple reflection in the cold-cathode tubes and also in theirglass tubes, and, as a result, the emitted light from the cold-cathodetubes can be efficiently led into the optical waveguide to therebyincrease the luminance of the backlight unit.

The backlight unit of this embodiment is described with reference to itsconcrete examples.

Example 1 of the Second Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 6. FIG. 6 is a cross-sectional viewseen in the same direction as that for FIG. 42. In this, however, onlythe region around the light source unit is shown. As in FIG. 6, thecold-cathode tubes 2, 4 are surrounded by the reflector 10 of which theinner surface is a reflective surface. Adjacent to the open end of thereflector 10, positioned is one end of the optical waveguide 1. Thoughnot shown in FIG. 6, the same light source unit as that illustratedherein is also provided adjacent to the opposite end of the opticalwaveguide. The diameter of each cold-cathode tube 2, 4 is 2.6 mm; andthe thickness of the optical waveguide 1 is 8 mm. The height of the openend of the reflector is 8.1 mm; and the end of the optical waveguide 1is disposed to overlap with the open end of the reflector by 0.1 mm orso.

The cold-cathode tubes 2, 4 are disposed almost in the center betweenthe reflector 10 and the end of the optical waveguide 1. Moreconcretely, the cold-cathode tube 4 is so disposed that its center axisis spaced from the bottom of the reflector 10 by a height of 2.3 mm andfrom the open end of the reflector 10 by 2.2 mm; and the cold-cathodetube 2 is so positioned that its center is spaced from the open end ofthe reflector 10 to the same level as that of the cold-cathode tube 4spaced from it, and is spaced by 3.6 mm from the center of thecold-cathode tube 4 directly above it. The cold-cathode tubes 2, 4 aredisposed in parallel with each other along the end of the opticalwaveguide 1. The distance between the cold-cathode tube 2 and thecold-cathode tube 4 is 1 mm.

The back side of the reflector 10 that is opposite to the open endthereof connected with the end of the optical waveguide 1 is modified tohave concaved curve segments C1, C2, C3, C4 seen from inside thereflector 10. Concretely, as in FIG. 6, the back side of the reflector10 is worked to form a curve segment C1 (radius R=3.2 mm) and a curvesegment C2 (radius R=4.0 mm) each having a curvature center, atpredetermined positions along the direction from the upper side to thelower side of the reflector 10. The curve segment C3 is formed nearly inthe center between the upper and lower sides of the reflector 10,symmetrically to the curve segment C2 relative to a virtual straightline drawn in parallel with the upper and lower sides of the reflector10; and the curve segment C4 is formed similarly to the curve segment C3but symmetrically to the curve segment C1.

In the optical source unit constructed in the manner as above, theessential ray La1 of the light emitted by the cold-cathode tube 2 in theradial direction of the cold-cathode tubes 2, 4 reaches the curvesegment C1 and is reflected thereon to run back through the spacebetween the cold-cathode tube 2 and the upper wall surface of thereflector 10. In this, the essential ray La2 of the light emitted by thecold-cathode tube 2 reaches the curve segment C2 and is reflectedthereon to run back through the space between the cold-cathode tube 2and the cold-cathode tube 4; and the essential ray La3 of the lightemitted by the cold-cathode tube 2 reaches the curve segment C3 and isreflected thereon to run back through the space between the cold-cathodetube 4 and the lower wall surface of the reflector 10.

Similarly, the essential ray Lb1 of the light emitted by thecold-cathode tube 4 reaches the curve segment C4 and is reflectedthereon to run back through the space between the cold-cathode tube 4and the lower wall surface of the reflector 10; the essential ray Lb2 ofthe light emitted by the cold-cathode tube 4 reaches the curve segmentC3 and is reflected thereon to run back through the space between thecold-cathode tube 2 and the cold-cathode tube 4; and the essential rayLb3 of the light emitted by the cold-cathode tube 4 reaches the curvesegment C2 and is reflected thereon to run back through the spacebetween the cold-cathode tube 2 and the upper wall surface of thereflector 10.

Of the emitted light running toward the back side of the reflector 10from the cold-cathode tubes 2, 4 in this Example, the rays toward thecurve segments C1, C2, C3 from the cold-cathode tube 2 and those towardthe curve segments C2, C3, C4 from the cold-cathode tube 4 can be allled into the optical waveguide 1, not going back into the cold-cathodetube 2 or 4.

Accordingly, since the light scattering and absorption to be caused bythe re-entrance of the reflected light into the cold-cathode tubes 2, 4,as well as the multiple reflection in the cold-cathode tubes and also intheir glass tubes can be minimized in the backlight unit of thisembodiment, the emitted light from the cold-cathode tubes 2, 4 can beefficiently led into the optical waveguide therein to thereby increasethe luminance of the backlight unit.

Example 2 of the Second Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 7. Like in FIG. 6, the region aroundthe light source unit to be in the backlight unit is shown in FIG. 7. Inthe light source unit shown in FIG. 7, the upper side of the reflector10 is worked to have concaved curve segments C6, C5 in that order seenfrom inside the reflector 10, in the direction toward the back side ofthe reflector 10 from the end of the optical waveguide 1. Concretely,the curve segment C6 is formed at a predetermined position, having acurvature center and having a radius R=3.21 mm; and the curve segment C5is formed also at a predetermined position, having a curvature centerand having a radius R=4.46 mm.

In this, the lower side of the reflector 10 is worked to have concavedcurve segments C6′, C5′ in that order seen from inside the reflector 10,in the direction toward the back side of the reflector 10 from the endof the optical waveguide 1. The curve segments C6′, C5′ are symmetric tothe curve segments C6, C5, respectively, relative to a virtual straightline drawn in parallel with the upper and lower sides of the reflector10 nearly in the center between the upper and lower sides thereof.

Except for its specific structure as above, the light source unit inthis Example is the same as that in Example 1 shown in FIG. 6. As thelight source unit is so constructed as herein, the light having reachedthe back side surface of the reflector 10 behaves like that inExample 1. In addition to this, the essential ray La4 of the lightemitted by the cold-cathode tube 2 reaches the curve segment C4 and isreflected thereon to reach the curve segment C5′. Then, this isreflected on the curve segment C5′ to run through the space between thecold-cathode tube 4 and the lower wall surface of the reflector 10. Theessential ray La5 of the light emitted by the cold-cathode tube 2reaches the curve segment C6 and is reflected thereon toward the opticalwaveguide 1. The same shall apply to the lower side surface of thereflector 10.

Since the light source unit in this Example is specifically constructedas above, not only the light analyzed and discussed in Example 1 butalso the light running toward the upper and lower side surfaces of thereflector 10 therein can be all efficiently led to the optical waveguide1. This Example realizes a backlight unit of higher efficiency than inExample 1.

Example 3 of the Second Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 8. Like in FIG. 6, the region aroundthe light source unit to be in the backlight unit is shown in FIG. 8.The light source unit shown in FIG. 8 comprises one cold-cathode tube 2and a reflector 10, and is characterized in that a second opticalwaveguide 36 is disposed between the cold-cathode tube 2 and thereflector 10.

A space is formed between the cold-cathode tube 2 and the second opticalwaveguide 36 and between the second optical waveguide 36 and thereflector 10, and an air layer is formed in this space. The secondoptical waveguide 36 is made of a transparent resin includingpolycarbonates, acrylic resins, etc., or is made of glass, and itsrefractive index is around 1.5. Almost all the light emitted by thecold-cathode tube 2 toward the back side of the reflector 10 enters thesecond optical waveguide 36, after having passed through the air layer(refractive index n=1). Having thus entered, the light passes throughthe second optical waveguide 36 and reaches its interface on the backside of the reflector 10.

On or through the interface of the second optical waveguide 36 on theback side of the reflector 10, the light is reflected or refracted, anda majority of the reflected light runs back through the second opticalwaveguide 36. The refracted light reaches the back side surface of thereflector 10 and is reflected thereon to run back toward the secondoptical waveguide 36, and reaches it. The light running through the endof the second optical waveguide 36 that faces the end of the firstoptical waveguide 1 enters the first optical waveguide through its end.

In the light source unit having the specific constitution as above, thecomponent of the light having entered the second optical waveguide 36but running back into the cold-cathode tube 2 can be reduced.Accordingly, the light source unit is free from the problem of lightscattering and absorption to be caused by the re-entrance of thereflected light into the cold-cathode tube 2, and from the problem ofmultiple reflection in the cold-cathode tube 2 and also in its glasstube; and the emitted light from the cold-cathode tube 2 can beefficiently led into the optical waveguide 1. With that, it is possibleto increase the luminance of the backlight unit of this Example.

Example 4 of the Second Embodiment

This Example is a modification of Example 3 and is characterized in thatthe profile of the second optical waveguide 36 adjacent to thecold-cathode tube is modified to be analogous to the outer profile ofthe cold-cathode tube. In the thus-modified structure, the emitted lightfrom the cold-cathode tube 2 enters the second optical waveguide 36nearly vertically thereto, and its surface reflection is thereforeminimized. Accordingly, the quantity of the light to enter the secondoptical waveguide 36 increases, and the light emission efficiency of thelight source unit is higher than that in Example 3. With that, it ispossible to further increase the luminance of the backlight unit of thisExample.

Example 5 of the Second Embodiment

This Example is another modification of Example 3. In this, the profileof the second optical waveguide 36 adjacent to the reflector is somodified that the interface between the second optical waveguide 36 andthe neighboring air layer ensures total light reflection thereon. Thatis, the interface between the second optical waveguide 36 (itsrefractive index is about 1.5) and the neighboring air layer (itsrefractive index is 1) enjoys total light reflection thereon when theincident angle thereto is at least 45°. Accordingly, not only thereflector 10 may be omitted in this unit but also 100% reflection can berealized therein even with the reflector 10 having a reflectance of 95%or so. Owing to such high reflection, the light emission efficiency ofthis unit can be increased.

To the same effect as above, a reflective film may be formed on thesurface of the second optical waveguide 36 that faces the reflector 10,and the same result as herein is expected.

According to this embodiment of the invention described hereinabove, thelight having been emitted by cold-cathode tubes toward a reflector canbe led into an optical waveguide via the space between the cold-cathodetubes and the reflector and via the space between the cold-cathode tubesadjacent to each other. Accordingly, the light emitted by thecold-cathode tubes can be efficiently led into the optical waveguide,high-luminance backlight units can be realized.

Next described is the backlight unit for liquid crystal displays andothers of the third embodiment of the invention with reference to FIG. 9through FIG. 21. This embodiment is to provide a backlight unit enoughfor practical use even though the light emission efficiency of thecold-cathode tubes therein is low. For this, we, the present inventorshave first analyzed the visible ray efficiency from optical viewpoints.As a result, we have found that, in the cold-cathode tubes describedhereinabove for the prior art technique with reference to FIG. 43, about30 to 50% of all the visible light emitted by the phosphor 138 entersthe glass tube 136, and the quantity of light that runs outside theglass tube 136 is extremely small, only about 5 to 20% of all.

Specifically, we have found that the light having been reflected on theouter surface of the glass tube 136 (refractive index: 1.5 or so) to goback to the discharge region is almost entirely absorbed by mercury,mercury gas and the phosphor existing therein or by the metal around theelectrodes therein, and this is one reason for light loss.

In addition, we have further found that the light having once goneoutside the glass tube 136 is, when reflected by the reflector 110 orthe like to go back to the outer surface of the glass tube 136,refracted to surely reach the phosphor 138 coated on the inner surfaceof the glass tube 136, and therefore nearly a half of the light isabsorbed by the phosphor 138 to cause light loss, and that the reflectedlight is almost completely scattered to further increase the light loss.

It is not realistic to reduce the size of the cold-cathode tubesthemselves so as to prevent them from interfering with the light thathas been reflected by the reflector 110 or the like to again pass aroundthe glass tube 136. The reason is because tubes having a smallerdiameter are heated more to have a higher temperature and the mercuryvapor concentration therein becomes higher, and therefore the increasein the UV rays to be absorbed becomes larger than the increase in the UVrays to be generated by mercury therein. As a result, with the decreasein the UV rays to be radiated to the phosphor, the amount of the visiblelight emission decreases, and the light source unit including thereflector becomes dark as a whole.

To reduce the loss as above and to increase the light utilizationefficiency, a transparent liquid, amorphous or solid substance, or thatis, such a transparent substance of which the refractive index is nearto that of the glass tube is filled in the space around the glass tubeto thereby optically seal up the outer surface of the glass tube withthat substance. In addition, the transparent liquid to be filled in thatspace is utilized as a coolant liquid, and the diameter (both the innerdiameter and the outer diameter) of the cold-cathode tubes is muchreduced without reducing the quantity of heat to be generated by thecold-cathode tubes. In this constitution, there occurs no or littletotal reflection in the interface between the glass tube (its refractiveindex is nearly 1.5) and the neighboring air space (its refractive indexis 1), and the constitution ensures the increase in light emissionefficiency of 30 to 50%.

The light having been reflected by the reflector or the like is, eventhough having reached the outer surface of the glass tube, goes straightor nearly straight ahead so far as it does not reach the inner surfaceof the glass tube, and can be taken out as the effective light. In thisconnection, for the diameter of cold-cathode tubes that interfere withlight passage, the outer diameter thereof must be taken intoconsideration in the prior art techniques. However, in this embodimentof the invention, the inner diameter of cold-cathode tubes that issmaller than the outer diameter thereof may be taken into considerationfor it. Therefore, the cold-cathode tubes to be used in this embodimentof the invention may be substantially thinner. One example of ordinarycold-cathode tubes has an outer diameter of 2.6 mm and an inner diameterof 2.0 mm.

In case where two such ordinary cold-cathode tubes are aligned inside arectangularly U-shaped reflector having a height of 6 mm, the lighthaving been reflected on the back side of the reflector to run towardthe end of the optical waveguide disposed in front of the reflector mustpass through the space between the two cold-cathode tubes and throughthe space between the ceiling surface or the bottom surface of thereflector and the cold-cathode tube neighboring to the reflector,concretely through the overall space of only 0.8 mm, in order that itcould be effective light. As opposed to this, however, in thisembodiment of the invention, the inner diameter of the cold-cathodetubes may be taken into consideration for the diameter thereof. In this,therefore, the space for light passage is substantially 2.8 mm, and thelight utilization efficiency of this embodiment is greatly increased.

In case where the space of the same level as in the example mentionedabove is kept as it is, the overall thickness of the light source unitcan be reduced by the wall thickness of the glass tubes of the twocold-cathode tubes, or that is, by 1.2 mm. Therefore, according to thisembodiment of the invention, the overall thickness, 8 mm, of theconventional light source unit can be reduced to 6.8 mm.

In addition, the diameter of the cold-cathode tubes in this embodimentof the invention can be reduced as they enjoy the coolant effectimparted thereto. Therefore, the effective light emission from the lightsource unit that includes a reflector can be increased. Accordingly,this embodiment of the invention realizes thinner light source units notdetracting from the brightness of the units.

The backlight unit of this embodiment is described hereinunder withreference to its concrete examples.

Example 1 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 9. FIG. 9 is a cross-sectional view ofa light source unit of a sidelight-type backlight unit, cut in the lightemission direction. In the light source unit of FIG. 9, cold-cathodetubes 102, 104 both having a conventional basic structure are disposedin a metallic housing 6, and the housing 6 is filled with a transparentliquid 8. The open end of the housing 6 is sealed up, for example, withan acrylic sheet 12. The inner surface of the housing 6 is coated with areflector 10.

In this Example, used is the metallic housing 6. Needless-to-say, thehousing 6 may also be made of transparent glass, plastics, etc. Thequantity of light emission from one cold-cathode tube 102 is small,falling between a few W and 10 W or so. In addition, since thecold-cathode tube 102 is long and thin, its heat radiation area can bebroad. Therefore, the member temperature can be lowered, concretely, 60°C. or lower.

For the transparent liquid 8, usable is any of water (refractive index:1.333), ethylene glycol (refractive index: 1.4318), glycerin (refractiveindex: 1.473), silicone oil such as phenyl-type silicone oil (refractiveindex: 1.403), silicone gel (refractive index: 1.405), siloxane-typeliquid, a mixture of glycerin 30% and ethylene glycol 70% (refractiveindex: 1.443), a mixture of water and ethylene glycol, mixtures of theseliquids, etc.

Also usable are fluorine-type inert liquids and the like, for example,insulating liquids such as Sumitomo 3M's perfluforocarbon liquids, etc.Since image formation is not intended in the invention, the refractiveindex distribution, if any, in the liquid owing to its temperaturedistribution involves few problems. All optical oils (matching oils),coolant oils, and other all transparent liquids are usable herein.Needless-to-say, sol-gel substances and others that can be filled inempty spaces are all usable herein.

The cold-cathode tubes 102, 104 are prepared by coating the innersurface of glass tubes having an outer diameter of 2.6 mm and an innerdiameter of 2.0 mm with a phosphor. The glass tubes are made ofborosilicate glass. Any other hard or semi-hard glass such as siliconglass or the like is also usable for them. For the phosphor, usable isany three-band phosphor prepared, for example, by mixing (SrCaBa)₅(PO₄)₃CL: Eu, LaPO₄:Ce,Tb, Y₂O₃: Eu and the like in a predeterminedratio. The glass tubes includes electrodes along with mercury, Ar andNe.

For the reflector 10, used is a high-reflectance film (mirror film).Also usable are inorganic members of aluminum or the like, as well asinterference reflectors such as multi-layered dielectric films, etc. Incase where the reflective surface of the reflector varies with time asit interacts with the liquid kept in contact with it, for example, whenthe reflective surface thereof reacts with or dissolves in the liquid,it may be coated with a hard coat of silicon oxide or the like forprotecting it. As the case may be, a reflective layer may be formedaround the outer surface of a glass container to be the reflector foruse herein.

The reflector 10 in this Example is formed to have a nearlyrectangularly U-shaped profile that follows the outer profile of thehousing 6, and the height of its open end is 6 mm and 8 mm for differenttwo types. In one type of the reflector 10 of which the height of theopen end is 6 mm, the space through which the light having beenreflected on the back side surface of the reflector 10 behind thecold-cathode tubes 102, 104 to run toward the open end of the reflector10 corresponds to the total of the space between the cold-cathode tube102 and the cold-cathode tube 104 and the space between the cold-cathodetube 102 or 104 and the reflector 10, and this is 2.0 mm in thisExample, but the space in the conventional structure (for example, as inFIG. 42) is 0.8 mm or so in total.

In the other type of the reflector 10 of which the height of the openend is 8 mm, the total of the space between the cold-cathode tube 102and the cold-cathode tube 104 and the space between the cold-cathodetube 102 or 104 and the reflector 10 is 4.0 mm in this Example, but is2.8 mm in the conventional structure (for example, as in FIG. 42).

As in FIG. 38, the light having been brought into contact with thecold-cathode tube 106 (108) is almost all reflected thereon to runtoward the opposite cold-cathode tube 108 (106), or will pass throughthe glass tube 136 to reach the phosphor 138, and nearly a half of it isabsorbed by the phosphor 138 or mercury in the glass tube 136 while theremaining half thereof is, after having been scattered, almostcompletely absorbed by the phosphor 138, etc., and disappears. Asopposed to this, in this Example, the rays 11, 12, 13, 14, 15 all gostraight ahead, not being refracted or reflected, as if the glass tube136 would not be present therein, as in FIG. 9. Accordingly, these rayscan go out directly through the open end of the reflector.

In addition, since the light from the phosphor 138 and the lightscattered thereon are reflected on the outer surface of the glass tube(its refractive index is nearly 1.5, and the total reflection anglethereto is around 42 degrees) in the conventional structure (see FIG.38), only about 20% of the light starting from the phosphor 138 could bego outside the glass tube. As opposed to this, almost 100% light can gooutside the glass tube in this Example.

Example 2 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 10. This Example differs from Example 1in that glass tubes 44 with a phosphor dispersed in their wall are usedherein for the cold-cathode tubes 40, 42. In this, the phosphor isdispersed in the wall of each glass tube as near as possible to theinner surface of the tube, whereby the substantial diameter of thecold-cathode tubes can be reduced. Even when the phosphor is disperseduniformly throughout the wall of each glass tube, the locallight-scattering ability of the glass tube is still low. In this case,therefore, the substantial diameter of the cold-cathode tubes can besmaller than the outer diameter of the glass tubes.

Example 3 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 11A and FIG. 11B. The light source unitin this Example is characterized in that the housing 6 filled with atransparent liquid 8 is provided with a temperature sensor 46, a heater48 for heating, and a Peltier device 50 for cooling, all disposed insideit. While being monitored with the temperature sensor 46, thetemperature inside the housing 6 is controlled to be on a predeterminedlevel by means of the heater 48 and the Peltier device 50. Thetemperature sensor 46 is disposed near to the most cooled part of thecold-cathode tube 102. While being monitored with the temperature sensor46, the most cooled part of the cold-cathode tube 102 is controlled tobe all the time on a predetermined level, whereby the mercury gas in thecold-cathode tube 102 can have a predetermined vapor pressure to ensurethe highest light emission.

Of the backlight units to be built in liquid crystal displays, some willbe disposed near to the minor sides of the display panel, while someothers will be near to the major sides thereof. In an ordinary mode ofusing displays, the display panel is inclined. In such a case, eitherone of the pair of minor sides and the pair of major sides is horizontalwhile the other one is inclined.

In this Example, when the cold-cathode tube 102 is disposedhorizontally, the temperature sensor 46 is disposed near to a part ofthe outer surface of the glass tube that is to be the most cooled part,and directly behind the reflector. In this, when the cold-cathode tube102 is disposed vertically (in FIG. 11A and FIG. 11B, the end B of thelight source unit faces below), the heater 48 is disposed at a suitableposition near the temperature sensor 46 and below it, and the Peltierdevice 50 is disposed at a suitable position above the temperaturesensor 46.

When the housing 6 is made of a metal material, it is cooled well as itsthermal conductivity is good. Therefore, the metallic housing 6 can bewell controlled at a predetermined temperature even though it is notequipped with a Peltier device.

It is effective to intentionally form the most cooled part of thecold-cathode tube at a predetermined position to thereby attain thetemperature control of the tube at that position. When the light sourceunit of this Example is built in a backlight unit and fitted to a liquidcrystal display, the outer periphery of the housing 6 except the areaaround the temperature sensor 46, the heater 48 and the Peltier device50 may be covered with a member having a low thermal conductivity, suchas a plastic sheet or the like having a thickness of at most 1 mm, sothat the housing 6 can be insulated from heat in some degree. Notlimited to the structure of this Example, the housing 6 may be soconstructed that it is covered with a closed vapor space capable ofsealing a vapor therein, or may be so constructed that it is protectedfrom air fluid flowing around it, and the housing 6 of such types alsoenjoys the same effect as herein. This applies to backlight units andliquid crystal displays equipped with a light source unit not having theabove-mentioned Peltier device to attain the same effect as herein.

Example 4 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 12. This Example is characterized inthat the housing 6 of Example 1 is provided with cooling fins 52 forheat radiation that run in the axial direction of the cold-cathode tube102 everywhere on the outer surface of the housing 6. The heat radiationfins 52 are provided in order to increase the surface area of thestructure, and may be of any type that meets the object. For example,they may be made of a material of good thermal conductivity to have agrooved surface, or may be made of a porous material of good thermalconductivity. The material of good thermal conductivity includes metalssuch as aluminum, copper, iron, etc.; carbon, graphite; resins with fineparticles or powder of such metal, carbon or graphite dispersed therein;electroconductive polymers such as polypyrrole, etc.

The profile and the distribution of the heat radiation fins 52 aredetermined, depending on the structure of the backlight with thecold-cathode tube 102 built therein and on the structure of the liquidcrystal display to be combined with the backlight. For example, theradiation fins 52 may be disposed only in the area around the center ofthe cold-cathode tube 102 in its axial direction, or only in the areaaround the temperature sensor 46 and the heater 48 and the Peltierdevice 50, or only in the area around the temperature sensor 46 and theheater 48. With the radiation fins 52 being so disposed, the site of themost cooled part of the cold-cathode tube 102 can be settled, and thetemperature of the most cooled part can be kept all the time constant.Accordingly, the quantity of light emission of the cold-cathode tube 102can be kept the largest.

Still alternatively, the number of the heat radiation fins 52 disposedin the area around the center of the cold-cathode tube 102 in its axialdirection, or in the area around the temperature sensor 46 and theheater 48 and the Peltier device 50, or in the area around thetemperature sensor 46 and the heater 48 may be increased; or the surfacearea of the fins in those areas is increased. With the radiation fins 52being so shifted, the site of the most cooled part of the cold-cathodetube 102 can be settled, and the temperature of the most cooled part canbe kept all the time constant. Accordingly, the quantity of lightemission of the cold-cathode tube 102 can be kept the largest.

Modification 1 of Example 4 of the Third Embodiment

An outline of the constitution of the backlight unit of thisModification is described with reference to FIG. 13. This Modificationis characterized in that cold-cathode tubes 102′, 104′ both having asmaller diameter than that of the cold-cathode tubes 102, 104 in FIG. 12are used in place of the tubes 102, 104. In this Modification, eventhough the diameter of the cold-cathode tubes used is small, thetemperature of the most cooled part of the tubes can be nearly on thesame level as that of conventional cold-cathode tubes having a largediameter, and the mercury vapor pressure in the tubes can be also nearlyon the same level as that of the conventional tubes. Therefore, theemission luminance of the cold-cathode tubes in this Modification may beon the same level as that of the conventional cold-cathode tubes.

In this Modification, the reflector 10 used has a rectangularly U-shapedprofile and the height of its open end is 8 mm. In this, since thecold-cathode tubes 102′, 104′ can be efficiently cooled, the innerdiameter of the tubes can be shortened to 1.5 mm, as compared with thatof the conventional cold-cathode tubes of which the inner diameter is2.0 mm, when the current to be applied to the tubes is from 5 to 8 mAlike conventionally to attain the light emission efficiency of the samelevel as that of the conventional tubes. As a result, in thisModification, the total of the space between the cold-cathode tube 102′and the cold-cathode tube 104′ and the space between the cold-cathodetube 102′ or 104′ and the reflector 10 may be 5.0 mm, though the totalspace is only 2.8 mm in the conventional structure as so mentionedhereinabove. Accordingly, the quantity of light emission from the openend of the reflector can be increased in this Modification, like inExample 1.

Modification 2 of Example 4 of the Third Embodiment

An outline of the constitution of the backlight unit of thisModification is described with reference to FIG. 14. In thisModification, the height of the housing 6 and the reflector 10 with thethin cold-cathode tubes 102′,104′ as in Modification 1 housed therein isso modified that the total of the space between the cold-cathode tube102′ and the cold-cathode tube 104′ and the space between thecold-cathode tube 102′ (104′) and the reflector 10 is the same as thatin the conventional structure with the conventional thick cold-cathodetubes 102, 104 housed therein.

As a result, the height of the reflector 10 is reduced to 5.8 mm in thisModification, though it is 8 mm in the conventional structure. Owing tothis effect, thinner backlight units and thinner liquid crystal displaysthan conventionally can be realized by this Modification. In addition,since the optical waveguide to be in this Modification can also bethinned, this Modification can realize more lightweight backlight unitsand more lightweight liquid crystal displays than conventionally.

Example 5 of the Third Embodiment

An outline of the constitution of this Example is described withreference to FIG. 15. This Example is characterized in that a thin andlong rectangular glass member 54 is used herein in place of the casing 6and the transparent liquid 8. Two cylindrical through-holes are formedthrough the glass member 54 in predetermined positions in the lengthwisedirection of the member; and a phosphor 138 is applied to the inner wallof each through-hole. The through-holes are filled with mercury, argonor the like and sealed up, and electrodes are inserted into the holesthrough their both sides and sealed up therein to construct thecold-cathode tubes 56, 58. The outer surface of the glass member 54 iscovered with a reflector 10. For the glass member 54, usable is hardglass such as borosilicate glass or the like.

Example 6 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 16. This Example is characterized inthat heat radiation fins 52 are provided on the outer surface of thereflector 10 in the structure of Example 5.

Like in Example 4, the heat radiation fins 52 are provided so as toincrease the surface area of the structure, and they may be of any typethat meets the object. For example, they may be made of a material ofgood thermal conductivity to have a grooved surface, or may be made of aporous material of good thermal conductivity. For the details of thematerial, referred to are the same as those in Example 4.

Like in Example 3, the temperature sensor 46, the heater 48 and thePeltier device 50; or the temperature sensor 46 and the heater 48 may beprovided in the area around the center of the cold-cathode tubes 56, 58in their lengthwise direction. For the profile and the distribution ofthe heat radiation fins 52, referred to are the same as in Example 3.

Example 7 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 17. In this Example, the light sourceunit of Example 1 is applied to a sidelight-type backlight, and amatching oil 14 is used to connect the light source unit to the opticalwaveguide 1.

The optical waveguide 1 may be made of any of polyacrylic acid,polycarbonate, glass, etc.

For the matching oil 14, usable is the same transparent liquid 8 as inExample 1. Preferably, the refractive index of the matching oil 14 isnear to the refractive index of the sealant 12 (this is to seal up theopen end of the light source unit) and to the refractive index of theoptical waveguide 1.

In this Example, the matching oil 14 is merely infiltrated into theinterface between the light source unit and the optical waveguide 1. Inaddition, the sides of the matching oil not facing the light source unitand the optical waveguide 1 may be surrounded by a solid wall, such as aglass container or the like, to thereby protect the matching oil fromoutside air and prevent it from being oxidized or vaporized. With that,the life of the oil may be prolonged. Further, the transparent liquid 8filled in the light source unit may be integrated with the matching oil14 so that the end of the optical waveguide 1 is integrated with theopen end of the light source unit. With that, the life of the oil mayalso be prolonged.

In this Example, used is the light source unit filled with thetransparent liquid 8. In place of this, the light source unit of a glassmaterial as in Example 5 may also be used in this Example to attain thesame effect as herein.

FIG. 18 is to explain the effect of this Example. This shows a virtualbacklight unit with the light source unit of this Example in the uppersite and with a conventional light source unit in the lower site. As inFIG. 18, the light having reached the light-emitting surface of theoptical waveguide at an incident angle of at least 42 degrees undergoestotal reflection on the surface. However, the light from theconventional light source unit that has entered the optical waveguide 1(its refractive index is around 1.5) through its end runs inside theoptical waveguide 1 while undergoing total reflection on thelight-emitting surface of the optical waveguide 1, but the light islimited to only that capable of reaching the light-emitting surface ofthe optical waveguide 1 at an incident angle of around 48 degrees ormore. On the other hand, in this Example, even the light that hasreached the light-emitting surface of the optical waveguide 1 at anincident angle of 42 degrees can pass through the optical waveguide.Therefore, in this Example, the optical waveguide accepts the lightexisting within a solid angle range broader by 1.31 times than that inthe conventional structure. Accordingly, the increase in the luminanceof the backlight unit of this Example by about 1.31 times that of theconventional backlight unit is expected.

Example 8 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 19. In this Example, heat radiationfins 52 are provided on the outer surface of the casing 6 in thestructure of Example 7. The effect of the heat radiation fins 52 is thesame as in Example 4, and its description is omitted herein.

Example 9 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 20. In this Example, through-holes areformed through the optical waveguide 1 at its one end, and the innersurface of the through-holes is coated with a phosphor. In addition, areflector 10 is formed on the outer surface of the optical waveguide 1at its end. Accordingly, in this Example, one end of the opticalwaveguide 1 is modified to form cold-cathode tubes 56, 58 through it, inplace the glass member 54 used in Example 5. Having this constitution,backlight units of high reliability can be realized.

Example 10 of the Third Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 21. The backlight unit of this Exampleis a direct-light-type backlight unit of which the structure is similarto that of FIG. 43 but differs from it in that a plurality ofcold-cathode tubes 102 a to 102 d are disposed in the space surroundedby the reflector 10 and its open end and that the space is filled with atransparent liquid 8 with the cold-cathode tubes being embedded in theliquid. Above the open end of the reflector 10, disposed is alight-diffusing device such as a diffuser, a prism array, a lens arrayor the like (not shown); and a polarizer and a liquid crystal aredisposed further over it to realize a liquid crystal display.

In this Example, since the thickness of the glass tubes 136 of thecold-cathode tubes 102 a to 102 d is optically negligible, theefficiency of light emission through the glass tubes 136 can be about 5times that in the conventional structure. Even when any light enters theglass tubes 136 of the cold-cathode tubes 102 a to 102 d, it can stillgo straight ahead so far as it does not meet the phosphor 138. In short,in the conventional light source unit, the size of the cold-cathodetubes is defined by the outer diameter of the glass tubes 136; but inthis Example, the inner diameter of the cold-cathode tubes 102 a to 102d corresponds to the substantial size of the cold-cathode tubes 102 a to102 d, and the size of the cold-cathode tubes 102 a to 102 d that arelight-shielding objects can be substantially reduced.

In addition, since the space surrounded by the reflector 10 and its openend is filled with the transparent liquid 8, and since the innerdiameter of the cold-cathode tubes 102 a to 102 d can be thereforereduced not detracting from their light emission efficiency, the size ofthe cold-cathode tubes can be further reduced. Moreover, since theliquid cools the reflector 10, it protects the reflector 10 from beingdeteriorated by heat. Accordingly, the life of the reflector 10 isprolonged. Not only it but also the life of the entire backlight unitand even the life of the liquid crystal display comprising the unit canbe prolonged.

In the Examples of this embodiment mentioned hereinabove, concretelydemonstrated are light source units with one or two cold-cathode tubestherein for sidelight-type backlight units, to which, however, theinvention is not whatsoever limited. Needless-to-say, even light sourceunits with three or more cold-cathode tubes therein surely display thefunctions and the effects described in the above-mentioned Examples.

In this embodiment of the invention described hereinabove, the lightemitted through the glass tubes of the cold-cathode tubes does notreflect on the outer surface of the glass tubes. Accordingly, the lightsource unit of this embodiment ensures light emission efficiency higherby about 5 times than that of conventional light source units. In thisembodiment of the invention, the light reflected on the reflector andalso the light emitted by the neighboring cold-cathode tubes all gostraight ahead, not interfered with by the glass tubes. Accordingly, inthis embodiment, the size of the light source unit can be determined onthe basis of the inner diameter of the cold-cathode tubes in the unit,though it is determined by the outer diameter of the cold-cathode tubesin conventional backlight units. Therefore, in the invention, the sizeof the light source unit can be substantially reduced.

In addition, owing to the coolant effect of the liquid filled in theunit, the vapor pressure of mercury in the cold-cathode tubes thatabsorbs UV rays and visible rays does not increase even when the tubesare down-sized. Therefore, the invention realizes increased lightemission efficiency of the unit. Moreover, since the cold-cathode tubesthat are optical obstacles or light-shielding objects can be down-sizedherein, the invention realizes efficiency-increased, wall-thinned andweight-reduced light source units, backlight units and liquid crystaldisplays. Further, since the reflector used herein is prevented frombeing deteriorated and since the other members not resistant to heat areall cooled by the liquid serving also as a coolant, the invention iseffective for prolonging light source units, backlight units and liquidcrystal displays.

Next described is the backlight unit for liquid crystal displays andothers of the fourth embodiment of the invention with reference to FIG.22A through FIG. 26B. This embodiment is to provide a backlight unitwith cold-cathode tubes having increased light emission efficiency.

The problem with the prior art 4 mentioned above is caused by the reasonthat the phosphor powder is not kept in airtight contact with the wall(glass) of the discharge tubes. To solve the problem, some measuresmentioned below are taken in this embodiment.

First, a transparent material with fluorescence centers introducedthereinto is used for the wall of discharge tubes. Next, thecold-cathode tubes are formed to have a tubular structure. This is inorder that the fluorescence centers introduced into the wall materialact as impurities to compensate for the reduction of the mechanicalstrength of the wall material.

Further, mercury is used for the UV source for discharge tubes. Mercuryhas the highest U emission efficiency, and is much used for UV sources.Alternatively, Xe or Ne is used for the UV source for discharge tubes.Discharge tubes comprising it release few harmful substances, ascompared with those comprising mercury, and the cost for discarding themcan be reduced.

Further, any of hard glass, quartz and metal halides that are almosttransparent to the luminescent line of mercury, 254 nm, is used for thewall of cold-cathode tubes. This is for enriching the UV rays that reachthe fluorescence centers in the wall made of it. For the fluorescencecenters to be introduced into the wall, used is a metal atom. For thefluorescent centers, also used is a mixture of a substance that absorbsUV rays and emits rays in a blue zone, and a substance that absorbs bluerays and emits visible rays in other wavelength ranges.

The wall is formed to have a multi-layered structure composed of aplurality of wall layers, in which each wall layer shall have at leastone type of fluorescence centers introduced thereinto. In this, thelayer nearer to a UV ray source shall have a blue-emitting substanceintroduced thereinto. In this, the concentration of each fluorescencecenter is so controlled that every light emission is unified for eachcolor. Accordingly, the emission balance of three primary colors isimproved to facilitate white balance. Every fluorescence center contentis so defined that it is inversely proportional to the quantum yield ofeach fluorescence center. In tubular discharge tubes, the number of thefluorescence centers is increased in the part corresponding to the darkUV emission part at their ends to thereby moderate the whitefluorescence luminance distribution.

Concrete structures of the cold-cathode tubes to be used in thebacklight unit of this embodiment are described with reference to theirexamples.

The combinations of the matrix material for the tubes and the substanceto be introduced thereinto that are illustrated in the followingdescription are some illustrative examples, to which, however, theinvention is not whatsoever limited. Needless-to-say, any othercombinations are usable herein for producing cold-cathode tubes,depending on the formulation of sensitizers used and on the color toneof the visible light to be emitted by the tubes. For example, substancestransparent to UV rays, such as CaF₂, MgF₂, LiF, NaF and the like arethe most suitable for the matrix material for the tubes; but for thefluorescence centers for conventional cold-cathode tubes, also suitableare glass materials such as quartz and silicon glass that transmitnear-UV rays (wavelength: 254 nm). In case where the fluorescencecenters are distributed relatively around the surface of the tubes, alsousable is hard glass.

In the following Examples, metal atoms (or ions) only are used for thefluorescence centers, which, however, are not limitative. Apart fromthis, also employable herein for the fluorescence centers is a method ofintroducing molecules such as CdS (this absorbs blue light and emitsorange color), etc., as well as ordinary phosphors, for example, finecrystals of Y₂O₃:Eu (the wavelength range of the fluorescence center isfor red), (SrCaBa)₅(PO₄)₃CL:Eu (the wavelength range of the fluorescencecenter is for green), LaPO₄:Ce,Tb (the wavelength range of thefluorescence center is for blue), etc.

In the following Examples, mercury is used for the UV source. Apart fromthis, also usable is Xe or Ar gas for the light source.

Example 1 of the Fourth Embodiment

Herein demonstrated is a cold-cathode tubes having a transparent memberof a metal halide, with reference to FIG. 22A through FIG. 22C. As inFIG. 22A, a transparent member 69 is disposed in the housing 66 of whichthe inner surface is coated with a reflective film 68 and which isfilled with nitrogen gas or dry air. The transparent member 69 iscomposed of a pair of polished, semi-spherical sheaths of grown lithiumfluoride crystal that are combined and adhered to each other with anoptical adhesive with two electrodes 60, 62 facing each other across thecenter of the member 69.

An inert gas (mixed gas of Ar and Ne) of around 0.1 atmospheres andmercury (Hg) are sealed up in the space 64 inside the spherical sheath.Into the transparent member 69, essentially introduced are F centers 70(minor M centers are formed through polymerization of the F centers 70).The F centers 70 are introduced into the member 69 according to acoloration method of heating the member 69 in a potassium metal vaporatmosphere.

As in FIG. 22A and FIG. 22B (this is a perspective view showing theoutline of the light source unit), a transparent window 72 is formedthrough the wall of the housing 66, and the emitted light from thetransparent member 69 inside the housing 66 is taken outside through thetransparent window 72. For the transparent window 72, used is atransparent sheet glass disc of which the diameter is nearly the same asthe diameter of the transparent member 69.

FIG. 22C is to show an outline of the method of introducing the Fcenters 70 into the transparent member 69. As in FIG. 22C, thetransparent member 69 is held in a container 75 for crystalintroduction, then the container 75 is put into an electric furnace 73,and the electric furnace 73 is heated to have an inner temperature ofabout 500° C. Next, the region 74 surrounded by the inner surface of thetransparent member 69 is filled up with potassium metal vapor. As aresult, the metal lithium vapor and the lithium fluoride crystal reachthermal equilibrium therebetween, and the F centers 70 having apredetermined concentration are thus formed. The discharge lamp thusfabricated to have the transparent member 69 therein is housed in thehousing 66 to finish the light source unit shown in FIG. 22A and FIG.22B.

Example 2 of the Fourth Embodiment

An outline of the constitution of the cold-cathode tube of this Exampleis described with reference to FIG. 23A and FIG. 23B. FIG. 23A is across-sectional view of a discharge tube, cut in the directionperpendicular to the axial direction of the tube. FIG. 23B is across-sectional view of the discharge tube, cut in the axial directionof the tube. The wall of the discharge tube is formed by adhering threeglass tubes to each other via an optical adhesive layer 91 existingbetween the neighboring glass tubes. A columnar Ni electrode 90 isfitted into the both ends of the tube along the axial direction of thetube. Regarding the profile and the material of the three glass tubes toform the cold-cathode tube, the outermost glass tube 78 is a silicaglass tube having an outer diameter of 3.0 mmφ and a wall thickness of0.2 mm; the interlayer glass tube 77 is a silica glass tube having anouter diameter of 2.6 mmφ and a wall thickness of 0.2 mm; and theinnermost glass tube 76 is a silica glass tube having an outer diameterof 2.2 mmφ and a wall thickness of 0.2 mm. The empty region 79surrounded by the innermost glass tube 76 is filled with a mixture of Negas, Ar gas and mercury gas, and this is sealed up.

Into these glass tubes 76, 77, 78, introduced are metal ions under thecondition mentioned below. Into the glass tube 78, introduced is asimple metal of Eu to have an Eu atomic molar concentration of 0.18%therein. Into the glass tube 77, introduced is a simple metal of Tb tohave a Tb atomic molar concentration of 0.94% therein. Into the glasstube 76, introduced is a simple metal of Mn to have an Mn atomic molarconcentration of 0.19% therein.

The metal introduced into each glass tube coordinates in the site of theSi atom in the glass. Eu in the glass tube acts to emit blue; Tb acts toemit green; and Mn acts to emit red. As a whole, they realize a lightsource of good color balance. As compared with the case where thesethree metals are introduced into one and the same glass tube, thethree-layered cold-cathode tube of this Example in which the threemetals are separately introduced into the three constituent glass layersis advantageous in that the individual fluorescence centers do notundergo energy transportation and ensure increased fluorescence emissionefficiency.

Example 3 of the Fourth Embodiment

An outline of the constitution of the cold-cathode tube of this Exampleis described with reference to FIG. 24A and FIG. 24B. FIG. 24A is aperspective view of a discharge tube cut in the direction perpendicularto the axial direction of the tube. FIG. 24B is a cross-sectional viewof the discharge tube, cut in the axial direction of the tube. The wallof this discharge tube is a quartz glass tube 80 having a wallthickness, b, of 0.7 mm. The empty region 79 surrounded by the glasstube 80 and having a diameter, c, of 2.0 mm is filled with a mixed gasof Xe and mercury that acts as a UV source, and this is sealed up.Accordingly, in the tube, a luminescent line appears at around awavelength of 150 nm.

In this Example, Eu, Tb and Mn atoms are introduced into the quartzglass tube 80 to a depth of the wall for 95% transmission of 185 nm UVray, or that is, to the wall depth, a, of 0.4 mm from the inner surfaceof the tube adjacent to the UV source. The atomic concentrationdistribution of the Eu, Tb and Mn atoms introduced into the quartz glasstube 80 to the depth of 0.4 mm from the inner surface of the tube isdescribed with reference to FIG. 25. In FIG. 25, the horizontal axisindicates the position in the quartz glass tube 80 varying in itslengthwise direction. The left-side vertical axis indicates the UVquantity; and the right-side vertical axis indicates the phosphorconcentration.

These metal atoms of Eu, Tb and Mn are introduced into the quartz glasstube 80 in such a controlled manner that their concentration isinversely proportional to the quantity of UV rays generated relative tothe lengthwise direction of the quartz glass tube 80 and is inverselyproportional to the quantum yield of each metal atom in light emission,as in FIG. 25.

Specifically, the fluorescence centers in this Example are a combinationof fluorescence centers to emit R (red) zone light, fluorescence centersto emit G (green) zone light, and fluorescence centers to emit B (blue)zone light; and they are characterized in that, when the quantum yieldsof these three types of fluorescence centers are designated by σ(R),σ(G) and σ(B), respectively, the product (optical density) of the meanconcentration of the fluorescence centers of each type and the depth ofthe wall of the glass tube into which the fluorescence centers of thetype are introduced is proportional to 1/σ(R), 1/σ(G) and 1/σ(B),respectively.

Example 4 of the Fourth Embodiment

Herein demonstrated is a cold-cathode tubes having a transparent memberof a metal halide, with reference to FIG. 26A and FIG. 26B. As in FIG.26A, a transparent member 69 is disposed in the housing 66 of which theinner surface is coated with a reflective film 68 and which is filledwith nitrogen gas or dry air. The transparent member 69 is composed of apair of polished, semi-spherical sheaths of grown potassium iodidecrystal that are combined and adhered to each other with an opticaladhesive with two electrodes 60, 62 facing each other across the centerof the member 69.

As in FIG. 26A and FIG. 26B (this is a perspective view showing theoutline of the cold-cathode tube), a transparent window 72 is formedthrough the wall of the housing 66, and the emitted light from thetransparent member 69 inside the housing 66 is taken outside through thetransparent window 72. For the transparent window 72, used is atransparent sheet glass disc of which the diameter is nearly the same asthe diameter of the transparent member 69.

The potassium iodide crystal used herein is crystallized with Ga and T1being therein at a concentration of around 10¹⁴ atoms/cm³ each. In theirabsorption→fluorescence emission cycle (zone A), these impurities haveabsorption/fluorescence emission zones at the peak wavelengths shown inTable 3.

TABLE 3 Absorption Zone and Emission Zone for Impurity Metal AtomsIntroduced into KI Crystal Peak Wavelength (nm) Impurity AtomsFluorescence Introduced Absorption Zone Emission Zone Ga 287, 291 502,608 T1 283 431

By controlling the concentration of these atoms to be in the transparentmember, cold-cathode tubes for emission of desired color balance can befabricated.

Of conventional cold-cathode tubes, the inner wall is coated with aphosphor, and the fluorescence centers of the phosphor are powderypolycrystalline particles. In the conventional cold-cathode tubes,therefore, the phosphor is seemingly non-transparent owing to irregularreflection and scattering of light on the surfaces of the fine crystalparticles therein. Being different to this conventional case, thefluorescence centers are introduced into the wall of the cold-cathodetube in the light source of this Example. The wall of the cold-cathodetube is colored with the fluorescent centers introduced thereinto, butis transparent. Therefore, as compared with the conventionalcold-cathode tubes, the light having again reached the wall of thecold-cathode tube of this Example passes through it or is reflected onit, not being scattered thereon. Accordingly, the light source unit ofthis Example ensures high emission efficiency. Concretely, the increasein light emission efficiency of the light source unit of this Examplemay be at most 18%.

Next described is the backlight unit for liquid crystal displays andothers of the fifth embodiment of the invention with reference to FIG.27 through FIG. 36. This embodiment is to provide a backlight unit withcold-cathode tubes having increased light emission efficiency.

In this embodiment, an emission tube for generating UV rays and a memberthat receives the thus-generated UV rays to emit visible light aredisposed in different spaces, and a UV reflector for reflecting the UVrays generated by the UV emission tube is provided, spaced from the UVemission tube. In this, the UV emission tube is spaced from the visibleemission tube, and the UV reflector is spaced from the UV emission tube.

Small light absorption, if so, in the emission tube does not increasethe tube temperature, therefore facilitating the reduction in the tubesize, and, as a result, the light that may reach the emission tube to bescattered by it as well as the light that may be absorbed by the vaporin the emission tube can be reduced, thereby realizing high-luminancebacklight units.

In this embodiment, the space surrounded by the UV reflector isextremely large relative to the size of the UV emission tube, andtherefore the quantity of the UV rays that re-enter the UV emission tubeis reduced. Accordingly, in this, the UV rays from the UV emission tubecan be most efficiently directed to the visible light takeout window.The UV emission tube in this embodiment is compared with a conventionalUV emission tube with respect to the visible light energy to be takenout of the tube as visible light. The data are shown below.

Comparison between the UV emission tube of this embodiment and aconventional UV emission tube with respect to the visible light energyto be taken out of the tube as visible light:

Prerequisites: UV energy generated in emission tube: A Luminousefficiency of phosphor: α = 0.4 Ratio of the quantity of light toscatter before 1/1 phosphor/the quantity of light to scatter afterphosphor: Transmittance of phosphor: β = 0.5 Transmittance of glass wallof emission tube: γ = 0.95 Reflectance of reflector: δ = 0.95Transmittance of vapor in tube: η = 0.85 Reflectance of UV reflector: σ= 0.95 Transmittance of visible light takeout window (in this ε = 0.95embodiment only):

Conventional UV emission tube:

(1) phosphor→glass wall of tube→reflector→visible light takeout window:

A·½·α·γ·δ=0.181A,

(2) phosphor→vapor in tube→phosphor→glass wall of tube→visible lighttakeout window:

A·½·α·η·β·γ+A·(½)²·α·η²·β·γ·δ+A·(½)⁴·α·η³·β·γ+A·(½)⁵·α·η⁴·β·γ·δ+ . . .=(0.0807+0.0325+0.0073+0.00294+ . . . )·A=0.124A,

Accordingly, (1)+(2)=0.305A.

UV emission tube of this embodiment:

vapor in tube→glass wall of tube→phosphor/reflector→visible lighttakeout window:

A·γ·½·α·(1+β·δ+(β·δ)²+(β+δ)³+ . . . )·ε=0.340A.

Accordingly, the ratio of visible light energy of the UV emission tubein this embodiment/visible light energy of conventional UV emissiontube=0.340A/0.305A=1.12.

This means that the increase in the visible light energy available inthe constitution of this embodiment is about 12% (however, the factorsof the constituent members used in the estimation made herein are notlimited to those mentioned above), or that is, the brightness of thebacklight source therein increases by about 12%.

The backlight unit of this embodiment is described with reference to itsconcrete examples.

Example 1 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 27. FIG. 27 is a cross-sectionalview of the light source unit of this Example, cut in the directionperpendicular to the axial direction of the emission tube in the unit.As in FIG. 27, the UV emission tube 81 with a mixed gas of mercury, Neand Ar sealed up therein is coated with neither phosphor nor UVabsorbent, and it is made of UV-transmitting glass (quartz, hard glass,etc.). For the UV/visible light reflector 82, for example, used is analuminum (Al) material having a reflectance of at least 90%, and thereflector 82 surrounds the emission tube 81 except a predetermined spacearound it, as in FIG. 27. If desired, the inner surface of theUV/visible light reflector 82 may be specifically processed for furtherincreasing its reflectance (for example, it maybe coated with a dichroiccoat).

In the part not surrounded by the UV/visible light reflector 82,provided is a UV reflector 85. The UV reflector 85 is, for example, atransparent glass substrate 83 (transparent sheet glass, Pyrex, etc.)coated with a UV reflective film 84.

Almost all the UV rays emitted by the UV emission tube 81 enter thevisible light emission member, for example, the phosphor 86 provided onthe inner surface of the UV/visible light reflector 82. The phosphor 86contains, for example, (SrCaBa)₅(PO₄)₃CL:Eu, LaPO₄:Ce,Tb, or Y₂O₃:Eu.This receives the UV rays and emits visible light. The visible lightthus emitted passes through the UV reflector 85 and goes outside thelight source unit.

On the other hand, the UV rays emitted by the UV emission tube 81directly toward the UV reflector 85 are reflected by the UV reflector 85to run toward the UV/visible light reflector 82, and enter the phosphor86 by which they are converted into visible light.

The UV/visible light reflector 82 has a parabolic profile in FIG. 27,but its profile is not limited to the illustrated one. So far as thevisible light is reflected on the inner surface of the UV/visible lightreflector 82 to go toward the UV reflector 85 and reach it to thehighest degree, the UV/visible light reflector 82 may have any desiredprofile. For example, its cross section may be square or oval.

Example 2 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 28. FIG. 28 is a cross-sectionalview of the light source unit of this Example, cut in the directionperpendicular to the axial direction of the emission tube in the unit.Like in Example 1, the space around the UV emission tube 81 issurrounded by the UV/visible light reflector 82, and a transparent glasssubstrate 83 is provided in the region through which the visible lightfrom the light source is taken out of the light source unit. On thesurface of the transparent substrate 83 that faces the UV emission tube81 is coated with a visible light emitter, for example with a phosphor86. The transparent substrate 83, when coated with nothing, may absorbUV rays, for example, it may be made of transparent sheet glass orPyrex.

Almost all the UV rays emitted by the UV emission tube 81 are reflectedby the UV/visible light reflector 82 to run toward the phosphor 86,which, after thus having received the UV rays emit visible light. SomeUV rays emitted will run toward the phosphor 86 directly from the UVemission tube 81, and these are also converted to visible light by thephosphor 86. In any case, the visible light passes through thetransparent substrate 83 and goes outside the light source unit. As thecase may be, the surface of the phosphor 86 (that faces the UVtransmission tube) may be coated with a visible light reflector 87 (forexample, with a dichroic coat capable of reflecting the rays fallingwithin a wavelength range of from 420 to 650 nm). In this case, all thevisible light emitted by the phosphor 86, including that running towardthe UV emission tube, is taken out of the light source unit.

Example 3 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 29A through FIG. 29C. FIG. 29A is aperspective view of the light source unit of this Example; and FIG. 29Bis a cross-sectional view of the light source unit seen in the directionof the arrow A drawn in FIG. 29A. FIG. 29C is a modification of thelight source unit, seen in the same direction as in FIG. 29B. Asillustrated, the UV emission tube 81 is long cylindrical; and aUV/visible light reflector 82 having a rectangularly U-shaped crosssection surrounds the UV emission tube 81, corresponding thereto.

The visible light-emitting side of the light source unit through whichthe visible light goes outside the unit (see FIG. 29A) extends in thelengthwise direction of the unit, corresponding to the lengthwisedirection of the UV emission tube 81. Accordingly, the UV rays emittedby the UV emission tube 81 can be efficiently converted into visiblelight. The constitution shown in FIG. 29B is the same as that of Example1 shown in FIG. 27, except that the cross section of the UV/visiblelight reflector 82 in the former has a rectangularly U-shaped profile.

Similarly, the UV emission tube 81 in FIG. 29C is long cylindrical, andthe configuration profile of the phosphor 86 extends long in thelengthwise direction of the unit, corresponding to the tube 82, so thatthe UV rays from the UV emission tube 81 are efficiently converted intovisible light. The constitution shown in FIG. 29C is the same as that ofExample 2 shown in FIG. 28, except that the cross section of theUV/visible light reflector 82 in the former has a rectangularly U-shapedprofile. Also in this modification, a visible light reflector 87 may beprovided on the surface of the phosphor 86 that faces the UV emissiontube, like in Example 2.

Example 4 of the Fifth Embodiment

An outline of the constitution of the backlight unit of this Example isdescribed with reference to FIG. 30A and FIG. 30B. FIG. 30A is across-sectional view of the light source unit of this Example, cut inthe direction perpendicular to the axial direction of the emission tubein the unit. FIG. 30B is a cross-sectional view of a modification of thelight source unit, cut in the direction perpendicular to the axialdirection of the emission tube in the unit. The UV emission tubes 81 inFIG. 30A and FIG. 30B are spherical. A UV/visible light reflector 82 isprovided to surround the space around the UV emission tubes 81, and thisis so inclined that the reflected light running toward it can beefficiently directed to the reflective surface 82′. The angle ofinclination is not indiscriminately determined, as depending on thelength of the reflective surface 82′, and it will be so defined that thequantity of visible light from the reflector 82 can be the largest.

A phosphor 86 is formed at least on the reflective surface 82′ in FIG.30A, but on the transparent glass substrate 83 that faces the reflectivesurface 82′ in FIG. 30B. Also in this Example, a visible light reflector85 may be provided on the phosphor 86 that faces the UV emission tubes81.

Example 5 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 31. FIG. 31 is a cross-sectionalview of the light source unit of this Example, cut in the directionperpendicular to the axial direction of the emission tube in the unit.The light source unit of this Example is characterized in that the innersurface of the wall of the UV/visible light reflector 82 that faces theUV emission tube 81 is corrugated or notched. In other words, the innersurface of the UV/visible light 82 is not planarized.

In the constitution as above, the UV rays emitted can be unified in thespace around the UV emission tube 81, and the visible light to beemitted by the phosphor 86 can be thereby unified. Needless-to-say, theinner surface of the UV/visible light reflector 82 in theabove-mentioned Examples 1 to 4 may also be modified like in FIG. 31.Also in this Example, the surface of the phosphor 86 that faces the UVemission tube 81 may be coated with a visible light reflector 87.

Example 6 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 32A and FIG. 32B. FIG. 32A and FIG.32B each are a cross-sectional view of the light source unit of thisExample, cut in the axial direction of the emission tube in the unit.The light source unit shown in FIG. 32A is characterized in that layersof red-emitting phosphor 86R, green-emitting phosphor 86G andblue-emitting phosphor 86B are alternately aligned on the inner surfaceof the UV/visible light reflector 82 therein.

On the other hand, the light source unit shown in FIG. 32B ischaracterized in that layers of red-emitting phosphor 86R,green-emitting phosphor 86G and blue-emitting phosphor 86B arealternately aligned on the inner surface of a transparent glasssubstrate 83 (for example, transparent sheet glass, Pyrex, quartz).

For the phosphors 86R, 86G, 86B, the same phosphor materials as those inExample 1 may be used. As not mixed with any other phosphor, eachphosphor 86R, 86G, 86B ensures excellent luminous efficiency. The sizeof the phosphor particles to be used and the thickness of the phosphorlayers to be formed shall be determined, taking the possibility ofprolonging the life of the phosphors 86R, 86G, 86B into consideration.For white balance, the area ratio of the phosphors 86R, 86G, 86B may bevaried. In FIG. 32B, a visible light reflector 87 may be provided on thesurfaces of the phosphors 86R, 86G, 86B that face the UV emission tube81.

In FIG. 32B, the neighboring phosphors 86R, 86G, 86B are in tightcontact with each other on the entire surface of the transparent glasssubstrate, but some of them may be omitted.

In this Example, the phosphors 86R, 86G, 86B are aligned directly asthey are, but they may be separately incorporated into UV-transmittablemembers. For example, quartz or fluorophosphates are used, and thephosphors are separately incorporated into melts of such substances.After the resulting melts are cooled and solidified, the solids areworked into a substrate having a predetermined shape. The technique ofincorporating phosphors into UV-transmittable members is applicable tothe above-mentioned Examples 1 to 5.

Example 7 of the Fifth Embodiment

An outline of the constitution of the backlight unit of this Example andthat of a liquid crystal display comprising the unit are described withreference to FIG. 33A and FIG. 33B. This Example is to demonstrate aliquid crystal display in which is used the backlight unit having thelight source unit of any of the above-mentioned Examples 1 to 6. FIG.33A is a perspective view of a liquid crystal display, which comprises aliquid crystal panel 134, an optical sheet 130, and a backlight unit(its optical waveguide 1 and light source unit are essentially shownherein) disposed in that order from its top.

A light source unit is disposed at one end of the optical waveguide 1,horizontally thereto. The visible light emitted in the light source unitpasses through the UV reflector 85 and enters the optical waveguide 1through its one end. In FIG. 33A, the light source unit is disposed onlyat one end of the optical waveguide 1, but it may be disposed at theboth ends thereof.

FIG. 33B is also a perspective view of a liquid crystal display, whichcomprises a liquid crystal panel 134, an optical sheet 130, and abacklight unit (its optical waveguide 1 and light source unit areessentially shown herein) disposed in that order from its top. Theliquid crystal display shown in FIG. 33B is characterized in that thelight source unit and the optical waveguide 1 are not at the same level,but each one at a different level in the oblique direction relative tothe other. The UV reflector 85 of the light source unit is connectedwith the optical waveguide 1 via a visible ray reflector sleeve 88provided therebetween, and the visible light having passed through theUV reflector 85 is, without being wasted, led into the optical waveguide1 after having passed through the visible light reflector sleeve 88.

Example 8 of the Fifth Embodiment

An outline of the constitution of the backlight unit of this Example andthat of a liquid crystal display comprising the unit are described withreference to FIG. 34. This Example is to demonstrate a liquid crystaldisplay in which is used the backlight unit having the light source unitof any of the above-mentioned Examples 1 to 6. FIG. 34 is a perspectiveview of a liquid crystal display, which comprises a liquid crystal panel134, an optical sheet 130, an optical waveguide 1 and a light sourceunit disposed in that order from its top.

In this Example, the backlight unit is a direct-light-type unit in whichthe light source unit is disposed below the optical waveguide 1. Inthis, a plurality of the light source units of any of Examples 1 to 6are aligned, with their UV reflectors 85 all facing the opticalwaveguide 1, to constitute one integrated light source unit. Being soconstituted, this realizes a high-efficiency direct-light-type backlightunit.

Example 9 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 35A through FIG. 35D. FIG. 35A is aperspective view of the light source unit of this Example. As in FIG.35A, a UV fluorescent lamp 81 is disposed inside the UV/visible lightreflector 82.

FIG. 35B is a cross-sectional view of the light-emitting side of theunit, cut in the direction perpendicular to the axial direction of theUV fluorescent lamp 81. As in FIG. 35B, the light-emitting side of theunit is in the form of a laminate composed of a visiblelight-reflective/UV-transmittable member 89 (this reflects visible lightand transmits UV rays) and a visible light emitter, for example, aphosphor 86.

Also as in FIG. 35B, the visible light-reflective/UV-transmittablemember 89 is formed of a UV-transmittable glass substrate 83 (forexample, quartz glass, etc.) of which the light-receiving surface iscoated with a dichroic coat 92 that transmits visible light and IR light(its transmittance is, for example, at least 90%). The light-emittingsurface of the glass substrate 83 (for example, quartz glass, etc.) iscoated with a phosphor 86.

FIG. 35C is a modification of the visiblelight-reflective/UV-transmittable member 89, seen in the same directionas that for FIG. 35B. In this modification, the dichroic coat 92 isformed on the both surfaces of the glass substrate 83; and thelight-emitting surface of the glass substrate 83 is further coated witha phosphor 86 via the underlying dichroic coat 92 therebetween.

The visible light-reflective/UV-transmittable member 89 is disposed toface the UV emission tube 81, as in FIG. 35A. In this structure, the UVrays emitted by the emission tube 81 are, directly or after having beenreflected by the UV/visible light reflector 82, reach the visiblelight-reflective/UV-transmittable member 89. At least 90% of the UV raysthus having reached the member 89 are, without being absorbed/reflected,enter the phosphor 86. With that, the phosphor 86 emits visible light. Apart of the thus-emitted visible light runs toward the UV emission tube81, but is reflected by the dichroic coat 92 formed on the visibleray-reflective/UV-transmittable member 89 and goes back to thelight-emitting direction.

FIG. 35D is another modification of the visiblelight-reflective/UV-transmittable member 89, seen in the same directionas that for FIG. 35B. This is composed of a dichroic coat 92 capable oftransmitting visible light only or transmitting visible light and IRlight, a glass substrate 83, a phosphor 86, and a visiblelight-transmittable/UV-reflective (or absorptive) member 93 in thatorder from the side facing the UV emission tube 81. The visiblelight-transmittable/UV-reflective (or absorptive) member 93 may be madeof, for example, a dichroic coat capable of transmitting light fallingwithin a wavelength range of from 420 to 650 nm and capable ofreflecting light of which the wavelength is not longer than 420 nm, ormay be made of a glass substrate capable of transmitting at least lightfalling within a wavelength range of from 420 to 650 nm and capable ofreflecting or absorbing light of which the wavelength is not longer than420 nm (transparent sheet glass, blue sheet glass, BK7 or SF-typeoptical glass or the like, and it may be further coated with an ARcoat).

Apart from the constitution mentioned above, a member of which therefractive index (real number or imaginary number) in the UV zone is farlarger than the refractive index (real number or imaginary number) inthe visible zone may be used for the visiblelight-reflective/UV-transmittable member 89.

Needless-to-say, the light source unit of this Example is applicable tothe backlight unit and the liquid crystal display of Examples 7 and 8.

Example 10 of the Fifth Embodiment

An outline of the constitution of the light source unit of this Exampleis described with reference to FIG. 36. FIG. 36 is a cross-sectionalview of the light source unit of this Example, cut in the directionperpendicular to the axial direction of the emission tube in the unit.This Example is characterized in that a part of the outer surface of theUV emitter 81 is coated with a phosphor 86′.

The region to be coated with the phosphor 86′ shall fall within therange of the angle formed by connecting the center point O of the UVemitter 81 with the two upper and lower edge points X, Y of the open endthrough which the visible light emitted is taken outside. Of the UV raysemitted by the UV emitter 81, those falling within the defined range areconverted into visible light by the phosphor 86′ provided on the outersurface of the UV emitter 81, and most of the thus-converted visiblelight runs toward the open end and is taken outside through it.Therefore, the visible light takeout efficiency of this constitution ishigh.

On the other hand, of the UV rays emitted by the UV emitter 81, thosenot falling within the defined range run toward the UV/visible lightreflector 82 that surrounds the open end, and are converted into visiblelight by the phosphor 86 provided on the reflective surface of theUV/visible light reflector 82. Then, the thus-converted visible light isreflected by the UV/visible light reflector 82, then runs toward theopen end and is taken outside. In FIG. 36, the range of the angle X-O-Yis defined, but is not limited to the illustrated area. The region ofthe UV emitter 81 to be coated with the phosphor 86′ may be controlledso as to realize the highest visible light takeout efficiency, dependingon the tube size of the UV emitter 81 and the size of the open end andalso on the size of the UV/visible light reflector 82.

In FIG. 36, one UV emitter 81 is used. If desired, a plurality of UVemitters may be used. The inner surface of the UV/visible lightreflector 82 is not limited to a flat one; and it may be coated withdifferent phosphors 86 for different emission zones.

As described hereinabove, the phosphor area can be enlarged to asatisfactory degree in this embodiment. Therefore, in this, the particlesize and the density of the phosphor particles to be used and also thethickness of the phosphor layer to be formed can be optimized to therebyprolong the life of the light source unit and increase the brightness ofthe unit. In addition, even when the emission tube used is downsized toreduce the overall thickness of the display unit comprising it, thephosphor area can still be kept large. Therefore, this embodimentrealizes thin-walled display devices, not detracting from theirbrightness.

As described in detail hereinabove with reference to its embodiments,the present invention realizes backlight units not involving the problemthat the emitted light leaks out of the optical waveguide, even when thespace around the cold-cathode tubes in the light source unit for them isfilled with a liquid of which the refractive index is nearly the same asthat of the glass material that forms the outer wall of the cold-cathodetubes.

In addition, in the invention, the light from the cold-cathode tubes isefficiently reflected toward the optical waveguide. Moreover, theinvention realizes backlight units enough for practical use even thoughthe luminous efficiency of the cold-cathode tubes therein is low.Further in the invention, the luminous efficiency of the cold-cathodetubes used is increased.

Sixth Embodiment of the Invention

The lighting unit of the sixth embodiment of the invention is describedwith reference to FIG. 46 to FIG. 68. Referring to FIG. 46, firstdescribed is the outline of the basic constitution of the lighting unitof this embodiment. FIG. 46 is a cross-sectional view showing theoutline of the lighting unit 401 of this embodiment, disposed adjacentto the surface of a flat panel FP such as a liquid crystal panel(hereinafter this is referred to as a liquid crystal panel as a genericterm) to be illuminated by it. The lighting unit 401 has a plurality ofoptical waveguides 406 a to 406 e that are spaced from each other. Onthe both sides of each of these optical waveguides 406 a to 406 e,disposed are a plurality of emission tubes (cold-cathode tubes) 402 a to402 f. The cold-cathode tubes 402 a to 402 f are on the side of the backsurfaces of the optical waveguides 406 a to 406 e that are opposite tothe light-emitting surfaces thereof adjacent to the surface of theliquid crystal panel FP to be illuminated by the lighting unit. Belowthe cold-cathode tubes 402 b to 402 e opposite to the liquid crystalpanel FP, provided are a plurality of reflectors 404 b to 404 e thatreflect the light from the cold-cathode tubes 402 b to 402 e toward theoptical waveguides 406 a to 406 e or directly toward the diffuser 408.On one side of each of the optical waveguides 406 a, 406 e, disposed arecold-cathode tubes 402 a, 402 f, and reflectors 404 a, 404 f. Thediffuser 408 is disposed between the optical waveguides 406 a to 406 eand the liquid crystal panel FP.

The lighting unit 401 of this embodiment having the basic constitutionas above may be considered as a backlight structure of a combination ofa side light-type unit and a direct-light-type unit, or may beconsidered as a backlight structure with a plurality of sidelight-typebacklight units aligned along the surface of the liquid crystal panelFP. In this basic structure illustrated, the number of emission tubescan be increased more than in a conventional sidelight-type backlightstructure, to thereby increase the luminance of the lighting unit.

In this structure, the cold-cathode tubes 402 a to 402 f are disposedbetween the optical waveguides 406 a to 406 e and they are on the sideof the back surfaces of the optical waveguides 406 a to 406 e that areopposite to the light-emitting surfaces thereof. In this, therefore,even if any of the cold-cathode tubes 402 a to 402 f are aged, theothers can still emit light and the thus-emitted light runs through theoptical waveguides 406 a to 406 e to compensate for the light quantityinsufficiency. For example, between the cold-cathode tubes 402 b, 402 c,the optical waveguide 406 b is disposed. Therefore, most of the lightemitted by the cold-cathode tube 402 b passes through the opticalwaveguide 406 b and illuminates the area around the neighboringcold-cathode tube 402 c. Accordingly, even if the cold-cathode tube 402c is aged and the quantity of light from it is lowered, the light fromthe other cold-cathode tubes 402 a, 402 b, 402 d, 402 e, etc. can passthrough the optical waveguides 406 a to 406 e and reaches the areaaround the cold-cathode tube 402 c. As compared with conventionaldirect-light-type backlight structures, therefore, the lighting unit ofthis embodiment is free from luminance fluctuation.

The lighting unit of this embodiment is described more concretely withreference to the following Examples.

Example 6-1

FIG. 47 is referred to for Example 6-1 of this embodiment. FIG. 47 is across-sectional view showing the outline of the lighting unit 401 ofthis Example, in which the lighting unit is disposed adjacent to thesurface of the liquid crystal panel FP to be illuminated by it. Thelighting unit 401 has a plurality of optical waveguides 406 a to 406 ethat are spaced from each other. On the both sides of the opticalwaveguides 406 b, 406 c, 406 d, disposed are cold-cathode tubes 402 b,402 c, 402 d, 402 e in that order. The structure of FIG. 47 differs fromthe basic structure of FIG. 46. In this, cold-cathode tubes 402 a, 402 fare not disposed on the outer side of the optical waveguides 406 a, 406e.

The reflector 404 (404 a, 404 b, 404 c, 404 d, 404 e and 404 f) may havethe same constitution as that of the reflector 110 in the conventionaldirect-light-type lighting unit shown in FIG. 43. As in FIG. 47, areflector 404 a is disposed adjacent to the left side of the opticalwaveguide 406 a; a reflector 404 c is adjacent to the right side of theoptical waveguide 406 e; and a reflector 404 b is disposed to entirelycover the lower surface of the lighting unit including the area of thecold-cathode tubes 402 b to 402 e. The reflector 404 b reflects thelight from the cold-cathode tubes 402 b to 402 e toward the opticalwaveguides 406 a to 406 e or directly toward the diffuser 409. In thisExample, two diffusers 408, 409 are disposed in parallel with each otherbetween the liquid crystal panel FP and the optical waveguides 406 a to406 e.

The outer diameter, d, of the cold-cathode tubes 402 b to 402 esandwiched between the optical waveguides 406 a to 406 e may be, forexample, d=2.6 mm. The optical waveguides 406 a to 406 e may be, forexample, thin acrylic plates having a size of 5 mm (thickness)×90 mm(width). The distance, d1, between the neighboring plates between whichthe cold-cathode tube 402 is sandwiched may be, for example, d1=5 mm.The reflectors 404 a to 404 c may be made of a reflective plate of whichthe inner surface that surrounds the optical waveguides 406 a to 406 eand the cold-cathode tubes 402 b to 402 e is white. The layered twodiffusers 408, 409 may be spaced from the optical waveguides 406 a to406 e, for example, by 20 mm.

For example, the light emitted by the cold-cathode tube 402 b is dividedinto two components, L1 that runs directly toward the diffusers 408, 409through the space between the optical waveguides 406 a and 406 b, and L2that enters the optical waveguide 406 b. The ratio of the quantity oflight of the component L1 to that of the component L2 will bedetermined, depending on the dimensional ratio of the optical waveguides406 a, 406 b to the cold-cathode tube 402 b. In this Example, thecomponent L1 accounts for about 40% of the emitted light, and thecomponent L2 accounts for the remaining, about 60% thereof, and thisenters the optical waveguides 406 a, 406 b through their side surfaces.

The component L2 having run through the optical waveguide 406 b isfurther divided into two components L3, L4, going further toward thediffusers 408, 409. The component L3 is, after having gone out of theoptical waveguide 406 b, enters the cold-cathode tube 402 c, on whichthis is scattered and reflected to run toward the diffusers 408, 409through the space between the optical waveguides 406 b and 406 c. Thecomponent 1, 4 is, after having gone out of the optical waveguide 406 c,directly led toward the diffusers 408, 409, through the space betweenthe optical waveguides 406 c and 406 d.

Like the light quantity ratio of L1:L2, the ratio of the component L3 tothe component L4 may be determined, depending on the dimensional ratioof the optical waveguides 406 to the cold-cathode tubes 402. In thisExample, the component L3 accounts for about 25%, and the component L4accounts for about 40%. The remaining 35% of the light enters the nextoptical waveguide 406 d, and runs in the same manner as before.

In the manner as described, the light emitted by the cold-cathode tube402 b reaches the neighboring cold-cathode tubes 402 c to 402 e via theoptical waveguides 406 a to 406 e, and runs toward the diffusers.Accordingly, the light running toward the diffusers through the spacebetween the optical waveguides 406 a to 406 e is not only the light fromthe cold-cathode tubes 402 b to 402 e themselves disposed in that spacebut also the light from the neighboring cold-cathode tubes 402 b to 402e.

The light having passed through the space between the optical waveguides406 a to 406 e goes on, while expanding, and enters the diffusers 408,409. The diffusers 408, 409 thus having received the light scatters itin every direction, while about ½ of the light having reached them isreflected and scattered by them. The reflected and scattered light isfurther reflected by the reflector 404 b via the optical waveguides 406a to 406 e and the cold-cathode tubes 402 b to 402 e, and then againpasses through the optical waveguides 406 a to 406 e and thecold-cathode tubes 402 b to 402 e to reach the diffusers 408, 409, and ahalf of the light thus having reached the diffusers 408, 409 is ledtoward the liquid crystal panel FP. In this case, the distance betweenthe diffusers 408, 409, the diffusing characteristics of the diffusers,the distance between the two diffusers and the reflector 404 b, and thedistance between the neighboring cold-cathode tubes 402 b to 402 e aresuitably controlled to evade luminance fluctuation in the lighting unit.

However, the characteristics of the cold-cathode tubes 402 b to 402 emay vary with the lapse of time, and may differ among the individualtubes. Therefore, though not so significant like those in conventionaldirect-light-type backlight structures, the cold-cathode tubes in thestructure of this Example not causing any problem in the initial stageof use will cause a problem of luminance fluctuation after used forlong. In this Example, a specific measure is taken to solve thisproblem. This is described below.

One case where the quantity of light from a certain cold-cathode tube402 is lowered to 70% is discussed with respect to the in-planeluminance fluctuation, comparing a backlight to which this Example isapplied with an ordinary direct-light-type backlight to which it is notapplied. (1) In the ordinary direct-light-type backlight unit, thequantity of light decreases to about 70%, and this light quantitydepression is nearly the same as that in the aged cold-cathode tube. (2)In the backlight of this Example, however, the quantity of lightdecreases to about 88%. This is because, though the light (40%) runningfrom the cold-cathode tubes 402 b to 402 e directly toward the diffusers408, 409 decreases to 28%, the quantity of light (60%) from theneighboring cold-cathode tubes 402 b to 402 e that runs through theoptical waveguides 406 a to 406 e does not vary. Accordingly, in thisExample, even when any of the cold-cathode tubes 402 b to 402 e is agedto emit a lowered quantity of light, its influence on the luminance ofthe lighting unit could be almost negligible, and, as a result, thelighting unit all the time ensures uniform light emission and has aprolonged life.

Example 6-2

Example 6-2 of this embodiment is described with reference to FIG. 48.FIG. 48 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. The lighting unit 401 of this Example is similar to but partlydiffers from that of Example 6-1, and this is characterized in that adiffusion pattern 410 of a diffusion layer which acts to vary the angleof the light running through the optical waveguides is provided on everyback surface of the optical waveguides 406 a to 406 e, and that, amongthe diffusers 408 and 409, the diffuser 409 is removed and only thediffuser 408 is provided. The other constituent elements of this Exampleare the same as those of Example 6-1, and describing them is thereforeomitted herein.

The light having been emitted by the cold-cathode tubes 402 b to 402 eand having entered the optical waveguides 406 a to 406 e run throughthem, while being totally reflected inside the optical waveguides 406 ato 406 e, but the light having entered the diffusion pattern 410 formedon every back surface of the optical waveguides 406 a to 406 e isdiffusively reflected. As a result, about ¼ of the light running throughthe optical waveguides does not satisfy the total reflection condition,and goes out through the light-emitting surfaces of the opticalwaveguides 406 a to 406 e to reach the diffuser 408. This is the sameprinciple as that in a conventional sidelight-type backlight structure.

For example, the light emitted by the cold-cathode tube 402 b runsthrough the optical waveguides 406 a to 406 e, whereby it can go out ina broad range, like the rays L1, L2. Similarly, the light emitted by thecold-cathode tubes 402 b to 402 e runs through the optical waveguides406 a to 406 e and reaches the diffuser 408 in a broad range.Accordingly, different rays having been emitted by the plurality ofcold-cathode tubes 402 b to 402 e are mixed on a point of the opticalwaveguides 406 a to 406 e and go out through it.

Controlling the size and the density of the diffusion pattern 410 willmake the optical waveguides 406 a to 406 e emit almost uniform lightthrough their light-emitting surfaces. Accordingly, in this Example,only one diffuser 408 will be enough for uniform light emission, thoughthe structure of Example 6-1 requires the two diffusers 408, 409. Ascompared with that in the structure of Example 6-1, the light componentthat goes out through the light-emitting surfaces of the opticalwaveguides 406 a to 406 e to reach the diffuser 408, not so muchinfluenced by the different light-emitting characteristics of thecold-cathode tubes 402 b to 402 e, increases in the structure of thisExample. Therefore, even though only one diffuser 408 is providedherein, the lighting unit of this Example is free from the problem ofluminance fluctuation to be caused by the individual difference in theintensity of light emission from the cold-cathode tubes 402 b to 402 eand by the time-dependent change of light emission from them.

Example 6-3

Example 6-3 of this embodiment is described with reference to FIG. 49 toFIG. 52. FIG. 49 is across-sectional view showing the outline of thelighting unit 401 of this Example, in which the lighting unit isdisposed adjacent to the surface of the liquid crystal panel FP to beilluminated by it. FIG. 50 is a partly enlarged view around thecold-cathode tube 402 c in this lighting unit. The lighting unit 401 ofthis Example is similar to but partly differs from that of Example 6-2,and this is characterized in that a diffuser 412 serving as alight-scattering element is disposed in the space sandwiched between thelight-emitting surfaces of the neighboring optical waveguides 406 a to406 e. The other constituent elements of this Example are the same asthose of Example 6-2, and describing them is therefore omitted herein.

In the structure of the above-mentioned Example 6-2, the density of thelight emitted by the cold-cathode tubes 402 b to 402 e to run directlytoward the diffuser 408 is larger than that of the light going towardthe diffuser 408 through the light-emitting surfaces of the opticalwaveguides 406 a to 406 e. In this Example, the diffuser 412 is disposedin the space sandwiched between the light-emitting surfaces of theneighboring optical waveguides 406 a to 406 e. The diffuser 412 reducesthe quantity of light directly running toward the diffuser 408 from thecold-cathode tubes 402 b to 402 e, to about ½, and the remaining, about½ of the light is diffused and reflected by the diffuser 412. Thethickness of the diffuser 412 is less than about ⅕ of that of theoptical waveguides 406 a to 406 e. Almost all the component of the lightreflected by the diffuser 412 enters the optical waveguides 406 a to 406e, and a part of it is scattered by the diffusion pattern 410 and goesout through the light-emitting surfaces of the optical waveguides 406 ato 406 e to reach the diffuser 408. In that manner, the differencebetween the density of the light to be emitted through thelight-emitting surfaces of the optical waveguides 406 a to 406 e andthat of the light to be emitted through the space between the opticalwaveguides 406 a to 406 e can be reduced, and, as a result, theinfluence of the difference in light emission between the cold-cathodetubes 402 b to 402 e on displays can be further reduced.

In this Example, the diffuser 412 is disposed in the space sandwichedbetween the light-emitting surfaces of the neighboring opticalwaveguides 406 a to 406 e. In place of the diffuser 412, an anisotropicdiffuser (anisotropic light-scattering element) of which thelight-diffusing ability varies depending on the direction of the lightentering it may be disposed in that space. In place of the thin diffuser412, such an anisotropic light-scattering element can diffuse the directlight from the cold-cathode tubes 402 b to 402 e to unify it, notinterfering with the passage of the light in the space between theoptical waveguides 406 a to 406 e, so far as the light running upwardthrough the space between the side edges of the optical waveguides 406 ato 406 e could be strongly diffused by it while that running from oneside edge of the optical waveguides 406 a to 406 e toward the other sideedge thereof is weekly diffused (if possible, not diffused).Specifically, the anisotropic light-scattering element is so definedthat it satisfies the relationship of A<B, in which A indicates thedegree of light scattering in the direction parallel to the surface ofthe display panel and B indicates the degree of light scattering in thedirection perpendicular to the surface of the display panel. Forexample, the anisotropic light-scattering element may be made of aliquid crystal polymer resin or the like that comprises a material ofrefractive anisotropy dispersively aligned in the matrix of norefractive anisotropy.

In this Example, the diffuser 412 capable of diffusing and reflectingabout ½ of the light having reached it is disposed in the space betweenthe neighboring optical waveguides 406 a to 406 e so as to reduce thequantity of the light that reaches the diffuser 408 through that space.In place of the diffuser 412, a reflector may be disposed in the space.FIG. 51 shows one example of using a reflector 414 in place of thediffuser 412. In this, the reflector 414 is disposed in the spacebetween the optical waveguides 406 a to 406 e in such a manner that thereflective surface of the reflector 414 is nearly at the same level asthat of the light-emitting surfaces of the optical waveguides 406 a to406 e. FIG. 51 is a partly enlarged view around the cold-cathode tube402 c. As illustrated, the reflector 414 is disposed in the spacebetween the optical waveguides 406 b, 406 c, nearly in the center of thespace, and this is nearly at the same level as that of thelight-emitting surfaces of the optical waveguides 406 b, 406 c. A spacecapable of passing the light L1, L2 therethrough is formed between thereflector 414 and the neighboring optical waveguides 406 b, 406 c. Inthat structure, a part of the light, L1, L2 emitted by the cold-cathodetube 402 c directly reaches the diffuser 408, while the remaining partthereof, L3, L4 reaches the optical waveguides 406 b, 406 c.

FIG. 52 shows another example of using a V-shaped reflector 416 in placeof the diffuser 412. As illustrated, the reflector 416 has a V-shapedreflective surface that faces the cold-cathode tubes 402 b to 402 e, andthis is disposed in the space between the optical waveguides 406 a to406 e. FIG. 52 is a partly enlarged view around the cold-cathode tube402 c. The reflector 416 is disposed in the space between thelight-emitting surfaces of the optical waveguides 406 b, 406 c, nearlyin the center of the space, and a space capable of passing the light L1,L2 therethrough is formed between the reflector 416 and the neighboringoptical waveguides 406 b, 406 c. In that structure, a part of the light,L1, L2 emitted by the cold-cathode tube 402 c directly reaches thediffuser 408, while the remaining part thereof, L3, L4 reaches theoptical waveguides 406 b, 406 c.

In the structures of FIG. 51 and FIG. 52, the difference between thequantity of the light to be emitted through the light-emitting surfacesof the optical waveguides 406 a to 406 e and that of the light to beemitted through the space between the optical waveguides 406 a to 406 ecan be reduced, and, as a result, the influence of the difference inlight emission between the cold-cathode tubes 402 a to 402 e on displayscan be further reduced.

Example 6-4

Example 6-4 of this embodiment is described with reference to FIG. 53 toFIG. 56. FIG. 53 is across-sectional view showing the outline of thelighting unit 401 of this Example, in which the lighting unit isdisposed adjacent to the surface of the liquid crystal panel FP to beilluminated by it. FIG. 54 and FIG. 55 each are a partly enlarged viewaround the cold-cathode tube 402 c in FIG. 53. The lighting unit 401 ofthis Example is similar to but partly differs from that of Example 6-2,and this is characterized in that the light-entering edge surfaces 418of the optical waveguides 406 a to 406 e with the diffusion pattern 410on their back surfaces are inclined. As in FIG. 53 to FIG. 55, thelight-entering surfaces 418 of the optical waveguides 406 a to 406 ebetween which the cold-cathode tubes 402 b to 402 e are sandwiched areso inclined that the distance between the light-emitting surfaces of theneighboring optical waveguides 406 a to 406 e is smaller than thatbetween the back surfaces thereof. The other constituent elements ofthis Example are the same as those of Example 6-2, and describing themis therefore omitted herein.

In this Example, the optical waveguides 406 a to 406 e are made of apolycarbonate plate having a refractive index n of not smaller than1.41. The polycarbonate plate is a thin plate having a thickness, t1, ofabout 8 mm, and its cross section is trapezoidal, having a width of thelight-emitting surface of 90 mm and a width of the back surface of 86.6mm. The light-entering edge surfaces 418 of the optical waveguides 406 ato 406 e are so inclined that they meet the back surfaces of the opticalwaveguides 406 a to 406 e (on which the diffusion pattern 410 is formed)at an angle, θ, of 102°. The distance, d2, between the back surfaces (onwhich the diffusion pattern 410 is formed) of the neighboring opticalwaveguides 406 a to 406 e is about 3.4 mm; and the thickness, t1, of theoptical waveguides 406 a to 406 e is about 8 mm. Therefore, theneighboring optical waveguides 406 a to 406 e are kept in contact witheach other at the edges of their light-emitting surfaces.

In Examples 6-1 to 6-3, a part of the light running through the spacebetween the optical waveguides 406 a to 406 e directly enters thediffuser 408. In the constitution of this Example, however, no lightrunning through that space directly enters the diffuser 408, but all thelight running through the space enters the optical waveguides 406 a to406 e. For example, as in FIG. 54, the angle, θ, formed by thelight-entering surface 418 and the back surface (on which the diffusionpattern 410 is formed) is 102° (=90°+12°). The light, L1, L2 emitted bythe cold-cathode tube 402 c will directly enter the diffuser 408 inExamples 6-1 to 6-3. In this, however, the light, L1, L2 enters theoptical waveguides 406 b, 406 c at an incident angle θ2, θ3 of at least51°, and the incident light satisfies the total reflection condition ofthe polycarbonate having a refractive index, n, of at least 1.59.Therefore, the optical waveguides in this Example can be dealt with inthe same manner as that for conventional optical waveguides. In thisExample, the optical waveguides 406 a to 406 e capable of emittinguniform light exist on the entire side below the diffuser 408.Therefore, the lighting unit of this Example realizes illumination ofextremely high uniformity.

As in FIG. 55, much of the light L3 having gone out of the opticalwaveguide 406 c to enter the optical waveguide 460 b is refracted in thedirection in which it avoids the cold-cathode tube 402 c. Therefore, thelight L3 emitted by the cold-cathode tube 402 c can be guided far awaythrough the optical waveguide 402 c, and the lighting unit of thisExample is free from the problem of luminance fluctuation to be causedby the individual difference in the intensity of light emission from thecold-cathode tubes 402 b to 402 e and by the time-dependent change oflight emission from them.

FIG. 56 shows a modification of the lighting unit of this Example, inwhich cold-cathode tubes 402 a, 402 f equipped with C-shaped reflectors404 a, 404 c, like in a sidelight-type backlight unit, are disposedoutside the two side optical waveguides 406 a, 406 e, respectively. Thismodification also enjoys the advantages of this Example.Needless-to-say, the constitution of this modification of FIG. 56,having the cold-cathode tubes 402 a, 402 f equipped with C-shapedreflectors 404 a, 404 c, may apply to the other Examples of thisembodiment.

Example 6-5

Example 6-5 of this embodiment is described with reference to FIG. 57.FIG. 57 is across-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. The lighting unit 401 of this Example is similar to but partlydiffers from that of Example 6-4, and this is characterized in that adiffusion pattern 410 is provided not on the back surfaces of theoptical waveguides 406 a to 406 e of the lighting unit 401 but on theback surface of a second optical waveguide 420 disposed between theoptical waveguides 406 a to 406 e and the diffuser 408, and that aphoto-bonding resin layer 422 is provided between the optical waveguides406 a to 406 e and the second optical waveguide 420. The otherconstituent elements of this Example are the same as those of Example6-4, and describing them is therefore omitted herein.

The second optical waveguide 420 has the same constitution as that of adiffusion pattern-coated optical waveguide in ordinary sidelight-typebacklight units. For example, it may be made of a polycarbonate plate ofwhich one surface is coated with a plurality of diffusion patterns 410.The photo-bonding resin layer 422 may be referred to as an opticaladhesive layer. Its refractive index, n, is nearly the same as that ofpolycarbonate, and its light transmittance is high. Via thephoto-bonding resin layer 422, the second optical waveguide 420 is stuckon the optical waveguides 406 a to 406 e.

Of the light having been emitted by the cold-cathode tube 402 b to enterand run through the optical waveguides 406 a to 406 e, for example, thecomponent L1, L2 that has reached the contact surface of thephoto-bonding resin layer 422 passes through the layer 422, not beingreflected thereon, and enters the second optical waveguide 420. On theother hand, the light running through the optical waveguides 406 a to406 e undergoes total reflection not in the area of the photo-bondingresin layer 422, and it does not run out toward the second opticalwaveguide 420. Therefore, the light runs toward the second opticalwaveguide 420 at high efficiency via the photo-bonding resin layer 422.The light of these components L1, L2 is guided inside the second opticalwaveguide 420, while being scattered by the diffusion pattern 410, andthus goes out through the light-emitting surface of the second opticalwaveguide 420 to reach the diffuser 408. In the constitution of thisExample, the cold-cathode tubes 402 b to 402 e almost completely losetheir locality. Therefore, the lighting unit of this Example is freefrom the problem of luminance fluctuation to be caused by the individualdifference in the intensity of light emission from the cold-cathodetubes 402 b to 402 e and by the time-dependent change of light emissionfrom them.

Example 6-6

Example 6-6 of this embodiment is described with reference to FIG. 58 toFIG. 64. FIG. 58 is a cross-sectional view showing the outline of thelighting unit 401 of this Example, in which the lighting unit isdisposed adjacent to the surface of the liquid crystal panel FP to beilluminated by it. FIG. 59 and FIG. 60 each are a partly enlarged viewaround the cold-cathode tube 402 c of FIG. 58. The lighting unit 401 ofthis Example is similar to but partly differs from that of Example 6-4,and this is characterized in that the reflector 404 b is so modified asto have recesses 424 below the cold-cathode tubes 402 b to 402 e. Inthis, the cold-cathode tubes 402 b to 402 e are housed in these recesses424. In the other Examples, the center axis of the cold-cathode tubes402 b to 402 e is nearer to the back surfaces of the optical waveguides406 a to 406 e than to the light-emitting surfaces thereof. In thisExample, the center axis of the tubes is far from the back surfaces ofthe optical waveguides 406 a to 406 e, relative to the light-emittingsurfaces thereof. The other constituent elements of this Example are thesame as those of Example 6-4, and describing them is therefore omittedherein.

In this Example, the cold-cathode tubes 402 b to 402 e are housed in therecesses 424, and the light emitted by them runs through the opticalwaveguides 406 a to 406 e, like L1 to L3 as in FIG. 59 and FIG. 60. Thelight L1 to L3 running in the space between the optical waveguides 406 ato 406 e is free from the interference, including reflection, refractionand absorption by the cold-cathode tubes 402 b to 402 e. In thisstructure, therefore, the loss of light L1 to L3 guided to remoteroptical waveguides 406 a to 406 e can be reduced.

The recesses 424 that characterize the constitution of this Example mayapply also to the above-mentioned Examples 6-1 to 6-5 and even to theother Examples of the other embodiments of the invention that will bementioned hereinunder. For example, the lighting unit 401 of FIG. 61 isa modification of the lighting unit 401 of FIG. 47 for Example 6-1. Thisis characterized in that the reflector 404 b is so modified as to havethe recesses 424 below the cold-cathode tubes 402 b to 402 e. In this,the cold-cathode tubes 402 b to 402 e are housed in the recesses 424.

Also having recesses 424, FIG. 62 is a modification of the lighting unit401 of FIG. 49 for Example 6-3. In this, the light L1 running throughthe optical waveguide 406 b toward the optical waveguide 406 c is notdisturbed by the cold-cathode tube 402 c and by the diffuser 412 c, asin FIG. 63. In that manner, the light L1 running through the opticalwaveguides 406 a to 406 e is well guided toward the neighboring ones.Accordingly, the light emitted by the cold-cathode tubes 402 b to 402 ecan be guided to remoter optical waveguides 406 a to 406 e, and thelighting unit of this modification is free from the problem of luminancefluctuation to be caused by the time-dependent change of light emissionfrom the cold-cathode tubes 402 b to 402 e.

Having recesses 424, FIG. 64 is a modification of the lighting unit 401of FIG. 52 for Example 6-3.

In the manner as above, the reflector 404 b can be readily modified tohave recesses 424 for housing the cold-cathode tubes 402 b to 402 etherein. In the modifications, the light running through the spacebetween the optical waveguides 406 a to 406 e is absorbed little by thecold-cathode tubes 402 b to 402 e. The modifications therefore realizedifferent types of lighting units in which the loss of light L1 to L3guided to remoter areas are reduced.

Example 6-7

Example 6-7 of this embodiment is described with reference to FIG. 65,FIG. 66A and FIG. 66B. FIG. 65 is a cross-sectional view showing theoutline of the lighting unit 401 of this Example, in which the lightingunit is disposed adjacent to the surface of the liquid crystal panel FPto be illuminated by it. The lighting unit 401 of this Example issimilar to but partly differs from that of Example 6-4 shown in FIG. 53,and this is characterized in that the back surfaces of the opticalwaveguides 406 a to 406 e are not provided with the diffusion pattern410 but are specifically worked to have a plurality of sharp recesses426 each having a triangular cross section. The cross section of thetriangular recesses 426 is an isosceles triangle of which the top angleis 70°. The back surfaces of the optical waveguides 406 a to 406 e areso worked as to have the triangular recesses 426 at a pitch of 1 mm, andthe a real ratio of the recesses 426 is 20%. The other constituentelements of this Example are the same as those of Example 6-4, anddescribing them is therefore omitted herein.

The triangular recesses 426 formed in the back surfaces of the opticalwaveguides 406 a to 406 e in this Example all functions as a diffusionelement that varies the angle of the light running through the opticalwaveguides, like the diffusion pattern 410 in Example 6-4. In this,however, the inclined surfaces of the triangular recesses act to diffuselight. Therefore, the light diffusion mode in this Example differs fromthat in Example 6-4 in which is formed the diffusion pattern 410. Thedifference in the light diffusion mode between them is described withreference to FIG. 66A and FIG. 66B. FIG. 66A shows the running mode ofthe scattered light in the optical waveguides 406 a to 406 e in theconstitution of Example 6-4 (only the optical waveguide 406 c is shown).A component L1 of the light running through the optical waveguide 406 creaches one dot of the dot-like diffusion pattern 410, and this isscattered thereon into a bundle L2 of a plurality of differentlyscattered rays, and further runs through the optical waveguide 406 c.The range of the angle of the light bundle L2 scattered on the dot ofthe diffusion pattern 410 is within a predetermined one that variesdepending on the incident angle of the light having reached the dot.Therefore, the light L3 that does not satisfy the total reflectioncondition but goes out through the light-emitting surface of the opticalwaveguide 406 c toward the diffuser 408 covers the majority of thecomponent that may slightly overstep the total reflection condition.Accordingly, the majority of the light L3 that goes out of the opticalwaveguide 406 c shall be nearly parallel with the light-emitting surfaceof the optical waveguide 406 c.

FIG. 66B shows the running mode of the scattered light in the opticalwaveguides 406 a to 406 e in the constitution of this Example (only theoptical waveguide 406 c is shown). While being guided through theoptical waveguide 406 c, the light bundle L1 is reflected once on theback surface of the optical waveguide 406 c, and reaches the inclinedsurface of the triangular recess 426, and it is then reflected on theinclined surface in the direction nearly perpendicular to thelight-emitting surface of the optical waveguide 406 c to give a bundleof scattered rays L2. The scattered light bundle L2 then goes out of theoptical waveguide 406 c to give a bundle of scattered rays L3 running inthe direction nearly perpendicular to the light-emitting surface of theoptical waveguide 406 c to reach the diffuser 408.

In the manner as above, the component of the light that goes out throughthe light-emitting surfaces of the optical waveguides 406 a to 406 e inthe oblique direction is large in the constitution in which thediffusion pattern 410 is disposed on the back surfaces of the opticalwaveguides 406 a to 406 e; while the component of the light that goesout in the direction of the normal line to the surface of the substrateis large in the constitution of this Example in which the triangularrecesses 426 are formed in the back surfaces of the optical waveguides406 a to 406 e. In the constitution of this Example, therefore, when thedisposition density of the triangular recesses 426 in the back surfacesof the optical waveguides 406 a to 406 e is distributed, it is easy toproduce light uniformly going out of the optical waveguides 406 a to 406e through their entire surfaces. In addition, in the constitution inwhich the diffusion pattern 410 is formed, an optical path-changingdevice is needed for changing the running direction of the light thatruns obliquely so that the light can run toward the surface of the panelto be illuminated by the lighting unit; while in the constitution ofthis Example in which the triangular recesses 426 are formed, such anoptical path-changing device is not needed since the light going out ofthe optical waveguides 406 a to 406 e runs all the time toward thesurface of the panel. Accordingly, in the constitution of this Example,the diffusion capability of the diffuser 408 may be low, and thelighting unit 401 of this Example realizes high efficiency at lowproduction costs. Needless-to-say, the triangular recesses 426 formed inthis Example may apply also to the back surfaces of the opticalwaveguides 406 a to 406 e in the other Examples of this embodiment toproduce the same results.

Example 6-8

Example 6-8 of this embodiment is described with reference to FIG. 67.FIG. 67 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. The lighting unit 401 of this Example is similar to but partlydiffers from that of Example 6-7 illustrated in FIG. 65, and this ischaracterized in that a reflective polarizer 428 which acts as areflection-type, optical path-changing element is disposed between thediffuser 408 of the lighting unit 401 and the surface of the liquidcrystal display panel FP to be illuminated by the lighting unit. Theother constituent elements of this Example are the same as those ofExample 6-7, and describing them is therefore omitted herein.

The reflective polarizer 428 has the function of selectivelytransmitting the light having been linearly polarized through it in apredetermined polarized direction but reflecting the light having beenpolarized in the other polarized direction. For the reflective polarizer428, for example, usable is 3M's DBEF or the like. In this Example, thetransmission polarization axis of the reflective polarizer 428corresponds to that of the liquid crystal panel FP which faces thereflective polarizer 428. The diffusion capability of the diffuser 408in this Example is lower than that of the diffuser 408 in Example 6-7.

The light L3 of which the majority runs in the direction nearlyperpendicular to the light-emitting surfaces of the optical waveguides406 a to 406 e, as in FIG. 66B illustrating the constitution of Example6-7, is scattered by the diffuser 408 of relatively low diffusioncapability, and then reaches the reflective polarizer 428. Thereflective polarizer 428 is so defined that its transmissionpolarization axis is parallel to the light source, and it reflects thecomponent of the light having been polarized in the direction thatdiffers from the direction of that axis. The reflected light L1 runstoward the diffuser 408, then runs through the optical waveguides 406 ato 406 e, and is reflected by the reflectors 404 a to 404 c, and thisagain reaches the reflective polarizer 428. Thus having run in thisroute, the reflected light L1 is disordered for its polarization, andbecomes almost non-polarized light. Accordingly, after a few times ofreflection and polarization cycles on and through the reflectivepolarizer 428, almost all the light emitted by the cold-cathode tubes ispolarized into linear polarized light to pass through the reflectivepolarizer 428. As so mentioned hereinabove, since the transmissionpolarization axis of the reflective polarizer 428 corresponds to that ofthe liquid crystal panel FP which faces the reflective polarizer 428,almost all the light from the reflective polarizer 428 contributes toimage display.

About a half of the light having reached the reflective polarizer 428 isreflected by it. Therefore, even though the light from the opticalwaveguides 406 a to 406 e is not uniform, the component of the lightfirst having passed through the reflective polarizer 428 and thecomponent of the light once reflected and then passing through it cancelthe luminance fluctuation. Accordingly, the luminance fluctuation in thelighting unit of this Example is reduced.

Even if the diffuser 408 in the constitution of this Example could notcompletely solve the luminance fluctuation, the lighting unit ensuressatisfactorily uniform illumination. Therefore, the diffusion capabilityof the diffuser 408 in this Example may be lower than that of thediffuser in Example 6-7. The combination of the diffuser 408 of lowdiffusion capability and the reflective polarizer 428 in this Examplerealizes high-efficiency backlight units.

Examples 6-9

Example 6 -9 of this embodiment is described with reference to FIG. 68.FIG. 68 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. The lighting unit 401 of this Example is similar to but partlydiffers from that of Example 6-5 illustrated in FIG. 57, and this ischaracterized in that a plurality of photo-bonding resin layers 422 aredisposed on the back surface of the second optical waveguide 420 in thearea thereof not coated with the plurality of diffusion pattern dots 410having a predetermined density. The other constituent elements of thisExample are the same as those of Example 6-5, and describing them istherefore omitted herein.

The light emitted by the cold-cathode tubes 402 b to 402 e reaches theoptical waveguides 406 a to 406 e and runs through them. However, thelight L1 having reached the light-emitting surfaces of the opticalwaveguides 406 a to 406 e that are in contact with the photo-bondingresin layers 422 enter the second optical waveguide 420, not reflectedon the interface between the light-emitting surfaces of the opticalwaveguides and the photo-bonding resin layer 422. The light runningthrough the optical waveguides 406 a to 406 e does not go out of theoptical waveguides 406 a to 406 e, but selectively goes out of themthrough the area of the photo-bonding resin layers 422, and, therefore,it efficiently enters the second optical waveguide 420. Running throughthe second optical waveguide 420, the light L1 reaches the diffusionpattern 410, and then goes out of the second optical waveguide 420 to bethe light L2, and this reaches the diffuser 408. In the constitution ofthis Example, the cold-cathode tubes 402 b to 402 e almost completelylose their locality. Therefore, the lighting unit of this Example isfree from the problem of luminance fluctuation to be caused by theindividual difference in the intensity of light emission from thecold-cathode tubes 402 b to 402 e and by the time-dependent change oflight emission from them.

As described with reference to its specific Examples, the lighting unitof this embodiment of the invention, in which a plurality ofcold-cathode tubes are disposed below the panel to be illuminated bythem, is free from the problem of luminance fluctuation to be caused bythe individual difference in the intensity of light emission from thecold-cathode tubes and by the time-dependent change of light emissionfrom them aged. Accordingly, this embodiment of the invention realizeshigh-power lighting units for uniform illumination.

Seventh Embodiment of the Invention

The lighting unit of the seventh embodiment of the invention isdescribed with reference to FIG. 69 to FIG. 77. This embodiment is forthe backlight structure for displays, and, in particular, it relates tothe structure of optical waveguides in sidelight-type backlight unitsthat illuminate liquid crystal panels from their back surface.

Transparent plastic substrates such as acrylic plates and the like areused for optical waveguides for conventional sidelight-type backlightunits. The plastic substrates include parallel-plate substrates having auniform thickness and wedged substrates of which the thickness nearer tolight source (emission tube) is larger than that remoter from it.

Parallel-plate substrates, if used for optical waveguides, must be thickin order that the optical waveguides can receive the light from lightsource at high-level light-utilization efficiency. On the otherhand,however, the substrates must be thin for thin, lightweight and low-costliquid crystal display panels. Accordingly, the tradeoff for thethickness reduction is inevitable in parallel-plate substrates. In thisrespect, parallel-plate substrates for optical waveguides areproblematic in that they could not satisfy all the requirements of highefficiency, weight reduction and cost reduction.

On the other hand, wedged substrates for optical waveguides require ahighly-accurate taper angle for their wedge form, because the lightrunning through the optical waveguides will gradually leak outside notundergoing total reflection. Therefore, reducing the production costsfor wedged substrates is impossible, and one problem with them is thatwedged substrates are unfavorable to large-sized backlight units. Theobject of this embodiment of the invention is to provide a small-sizedand lightweight lighting unit that realizes high-level light-utilizationefficiency and can be produced at low costs.

The optical waveguide in the lighting unit of this embodiment is made ofa parallel-plate substrate as a whole, but is characterized in that thearea around the light-entering surface SO of the side edge of theoptical waveguide that receives the light emitted by a light source isinclined. The inclined part is made of a material of which therefractive index is the same as that of the parallel-plate substrate.

The inclined part has an inclined surface that ascends from the surfaceof the parallel-plate substrate (this is the light-emitting surface ofthe optical waveguide or the back surface opposite to it) toward thelight-entering surface SO of the optical waveguide. The angle betweenthe inclined surface and the surface of the parallel-plate substrate(this is hereinafter referred to as an angle of inclination) is sodefined that the light having entered the inclined part through thelight-entering surface SO can undergo total reflection on the inclinedsurface and thereafter can also undergo total reflection in the area ofthe parallel-plate substrate.

The length of the inclined surface in the cross section cut along theplane perpendicular to both the inclined surface and the surface of theparallel-plate substrate (this is hereinafter referred to as a length ofinclination) is so defined that the incident light having passed throughthe light-entering surface SO does not hit the inclined surface twice ormore.

With the inclined part provided at the edges of the optical waveguide,the open area of the reflector that surrounds the light source, or thatis, the area of the light-entering surface SO of the optical waveguidecan be enlarged and the light-utilization efficiency of the lightingunit can be thereby enhanced. For the light-utilization efficiency ofthe same level, the thickness of the parallel-plate substrate of theoptical waveguide can be reduced.

The lighting unit of this embodiment is described more concretely withreference to the following Examples.

Example 7-1

FIG. 69 and FIG. 70 are referred to for Example 7-1 of this embodiment.FIG. 69 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. The lighting unit 401 has a light source 434 and an opticalwaveguide 436. In addition, the lighting unit 401 further has areflector, a diffuser sheet, etc. However, these are unnecessary fordescribing this Example. Unless specifically needed, therefore,describing and illustrating them is omitted in the section of thisembodiment.

The light source 434 has a cold-cathode tube 402 and a reflector 404.The optical waveguide 436 has a parallel-plate substrate 406 made of atransparent plate such as an acrylic resin plate or the like; andinclined parts 430, 432 provided around the light-entering surface SO atthe edge of the parallel-plate substrate 406 that receives the lightfrom the light source 434 through the open end of the reflector 404. Theinclined parts 430, 432 are made of the same material of theparallel-plate substrate 406. The parallel-plate substrate 406 isdisposed nearly parallel to the surface of the liquid crystal panel FPto be illuminated by the lighting unit. In this embodiment, the surfaceof the parallel-plate substrate 406 that is nearer to the surface of theliquid crystal panel FP is the light-emitting surface, and the surfacethereof that is remoter from it is the back surface.

The inclined part 430 is formed on the light-emitting surface of theparallel-plate substrate 406, and this has an inclined surface 430 athat ascends toward the light-entering surface SO. The angle ofinclination, α, of the inclined part 430 is so defined that the lighthaving entered the inclined part 430 via the light-entering surface SOundergoes total reflection on the inclined surface 430 a and thereafterundergoes total reflection also in the area of the parallel-platesubstrate 406. Similarly to this, the inclined part 432 also has aninclined surface 432 a at an angle of inclination, α, and this is formedon the back surface of the parallel-plate substrate 406.

The length of inclination, l, of the inclined parts 430, 432 is sodefined that the incident light from the light-entering surface SO doesnot hit the inclined surfaces 430 a, 432 a twice or more. Thelight-entering surface SO includes the edge surface of the inclinedparts 430, 432 facing the light-entering surface SO, and the edgesurface of the parallel-plate substrate 406 also facing thelight-entering surface SO. These edge surfaces are nearly in the sameplane.

The illumination mode of the lighting unit 401 of this Example isdescribed with reference to FIG. 70. FIG. 70 graphically shows how andin what manner the light from the light source 434 runs through theoptical guide 436. First, the light L1 from the light source 434 reachesthe light-entering surface SO at an incident angle falling between 0°and 90°. FIG. 70 shows the light L1 incident on the surface SO at theincident angle about 90°. The refractive index of the optical waveguide436 is represented by n. The incident light L1 is refracted on thelight-entering surface SO at an angle of refraction falling between 0°and (90°−θ), depending on the refractive index, n, and thethus-refracted light L2 then runs through the optical waveguide 436. θindicates the incident angle of the refracted light L2 having reachedthe inclined surface 430 a or the inclined surface 432 a, when the angleof inclination, α=0. In FIG. 70, the optical path length of Light L2 isalmost 0.

The refractive index of air, n0=1.0. The Snell's law and the totalreflection condition apply to the light-entering surface SO.

Accordingly,

n·sin (90°−θ)=n0·sin (90°)=1.

Therefore,

(90°−θ)=sin⁻¹ (l/n)  (1)

The angle of inclination, α, of the inclined parts 430, 432 is sodefined that the light L2 having entered the optical waveguide 436undergoes total reflection on any of the inclined surface 430 a or theinclined surface 432 a, and thereafter further undergoes totalreflection in the area of the parallel-plate substrate 406. For example,the light L3 having undergone total reflection on the inclined surface430 a does not reach the opposite inclined surface 432 a but reaches theback surface of the parallel-plate substrate 406, and thereafter thisruns through the parallel-plate substrate 406 while repeatedlyundergoing total reflection therein. Similarly, the light totallyreflected on the inclined surface 432 a does not reach the oppositeinclined surface 430 a but reached the back surface of theparallel-plate substrate 406, and thereafter this runs through theparallel-plate substrate 406 while repeatedly undergoing totalreflection therein.

The length of inclination, l, of the inclined parts 430, 432 is sodefined that all the incident light having entered the optical waveguidethrough the light-entering surface SO and having undergone totalreflection on one inclined surface 430 a (432 a) does not hit the otherinclined surface 432 a (430 a).

For attaining the best result in this Example, it is desirable that theangle of inclination, α, of the inclined parts 430, 432 is larger andthat the length of inclination, l, thereof is shorter. In practice,therefore, the parameters are defined so as to satisfy the relationalformulae mentioned below. A case where the refracted light L2 reachesthe inclined part 430 as in FIG. 70 is referred to by way of example.

In this,

h indicates the thickness of the parallel part of the parallel-platesubstrate 406;

n indicates the refractive index of the optical waveguide;

Δh indicates the height of the inclined part 430 standing on theparallel-plate substrate 406 at its light-entering surface SO;

Δ=n·Δh (=optical distance).

When the light L1 is refracted on the light-entering surface SO at anangle of refraction, (90°−θ) and the thus-refracted light L2 reaches theinclined surface 430 a of which the angle of inclination is α, then theincident angle of the refracted light L2 to the inclined surface 430 ais represented by θ−α. The total reflected light L3 reflected on theinclined surface 430 a reaches the back surface of the parallel-platesubstrate 406 at an incident angle, θ−2α. Accordingly, in order that thelight L2 having entered the optical waveguide 436 undergoes totalreflection on the inclined surface 430 a and then further undergoestotal reflection also in the area of the parallel-plate substrate 406,the angle of inclination, α, of the inclined part 430 must satisfy theformula (2) mentioned below. Based on the Snell's law and the totalreflection condition,

n·sin (θ−2α)≧n0·sin (90°)=1.

Accordingly,

n·sin (θ−2α)≧1  (2).

On the other hand, in order that the incident light having passedthrough the light-entering surface SO does not hit the inclined surface430 a, 432 a twice or more, the length of inclination, l, of theinclined part 430, 432 must satisfy the formula (3) mentioned below.Referring to FIG. 70,

(n·h+Δ)·tan (θ)=n·l·cos (α).

Accordingly,

(h+Δh)·tan (θ)=l·cos (α)  (3).

Further referring to FIG. 70,

n·l·sin (α)=Δ.

Accordingly,

l·sin (α)=Δh  (4).

From the formula (1),

n·cos (θ−α)=1  (5).

In this Example, the optical waveguide 434 is made of acrylic resin. Theacrylic resin has a refractive index, n=1.49. Accordingly, from theformula (1), θ=47.84°. This value of θ is introduced into the formula(2), and the angle of inclination, α=5.680.

The thickness of the parallel part of the parallel-plate substrate 406,h=10 mm; the height of the inclined part 430 standing on theparallel-plate substrate 406 at its light-entering surface So, Δh=0.6mm; and these values are introduced into the formula (3) to obtain thelength of inclination, l. This is as follows:

l=(10+0.6)·tan (47.84°)/cos (5.68°)=11.76 mm.

As compared with a case of using a conventional parallel-plate opticalwaveguide having a thickness of 10 mm, the width of the open end of thereflector 404 can be increased by 1.2 mm (=2·Δh) in this Example.Accordingly, in this Example, the quantity of light that may be led intothe optical waveguide 436 can be increased by 8%, as compared with theconventional case. Therefore, in this, the reflector 404 can be spacedmore from the cold-cathode tube 402, and the light emitted by thecold-cathode tube 402 toward the reflector 404 can be more readily ledto the optical waveguide 436. In this Example illustrated, theparallel-plate substrate 406 and the inclined parts 430, 432 are madeseparately. However, the invention is not limited to this illustration.The parallel-plate substrate 406 and the inclined parts 430, 432 may bebonded together via an adhesive therebetween, all having nearly the samerefractive index; or they may be integrated into a monolithic structure.

Example 7-2

Example 7-2 of this embodiment is described with reference to FIG. 71and FIG. 72. FIG. 71 is a cross-sectional view showing the outline ofthe lighting unit 401 of this Example, in which the lighting unit isdisposed adjacent to the surface of the liquid crystal panel FP to beilluminated by it. In this, the same constituent elements as those inExample 7-1 are designated by the same reference numerals, anddescribing them is omitted herein. The lighting unit 401 of this Exampleis similar to but partly differs from that of Example 7-1, and this ischaracterized by having only the inclined part 432, not having theinclined part 430. In this, the inclined part 432 stands on the backsurface (this is the inclined part-standing surface) of theparallel-plate substrate 406, extending from the light-entering surfaceSO of the substrate 406.

This Example is further characterized in that the light-entering surfaceSO is so worked that the inclined part-standing surface and thelight-entering surface SO of the parallel-plate substrate 406 meet at anobtuse angle. The angle formed by the perpendicular line dropped fromthe light-emitting surface of the parallel-plate substrate 406 towardthe back surface thereof, and the light-entering surface SO thereof isreferred to as an angle of inclination, β. Contrary to the illustration,the inclined part 432 may be omitted to form a structure having theinclined part 430 only. Needless-to-say, this structure ensures the sameeffect as that of the structure illustrated. Also in the non-illustratedstructure, the light-entering surface SO of the parallel-plate substrate406 is so worked that it meets the light-emitting surface (this is theinclined part-standing surface) thereof at an obtuse angle. Anyhow, thisExample is characterized in that the inclined part stands on either oneof the light-emitting surface or the back surface of the parallel-platesubstrate 406, extending from the light-entering surface SO of thesubstrate 406.

Next described is the illumination mode of the lighting unit 401 of thisExample with reference to FIG. 72. FIG. 72 shows how and in what mannerthe light from the light source 434 runs through the optical waveguide436. A majority of the light, L5, having entered the optical waveguide436 runs toward the surface not provided the inclined part 432 thereon.The angle of inclination, β, is so defined that all the light L5 couldbe the light L6 that undergoes total reflection on the light-emittingsurface and the back surface of the parallel-plate substrate 406. Thelength of inclination, l, is so defined that the light L5, which runsthrough the optical waveguide while undergoing total reflection, doesnot hit the inclined part 432.

A part of the light, L1, having entered the optical waveguide throughits light-entering surface SO runs toward the inclined part 432, asillustrated. The angle of inclination, α, is so defined that the lightL1 undergoes total reflection on the inclined surface 432 a, and, afterhaving been thus totally reflected thereon, further undergoes totalreflection also on the light-emitting surface and the back surface ofthe parallel-plate substrate 406. The light L2 thus having undergonetotal reflection on the inclined surface 432 a of the inclined part 432gives the light L3, and the light L3 thereafter runs through the opticalwaveguide while repeatedly undergoing total reflection on thelight-emitting surface and the back surface of the parallel-platesubstrate 406.

For attaining the best result in this Example, it is desirable that theangle of inclination, β, and the angle of inclination, α, are bothlarger, and that the length of inclination, l, is shorter. In practice,therefore, the parameters are defined so as to satisfy the relationalformulae mentioned below. A case where the refracted light L2 reachesthe inclined part 432 as in FIG. 72 is referred to by way of example.

First, the incident light L1 from the light source 434 reaches thelight-entering surface SO at an incident angle falling between β and(90°+β). The refractive index of the optical waveguide 436 isrepresented by n. The incident light L1 is refracted on thelight-entering surface SO at an angle of refraction falling between βand (90°+β−θ), depending on the refractive index, n, of the opticalwaveguide 436, and the thus-refracted light L2 then runs through theoptical waveguide 436. θ indicates the incident angle of the refractedlight L2 having reached the inclined surface 432 a, when the angle ofinclination, α=0. Accordingly, when the light L1 is refracted on thelight-entering surface SO at an angle of refraction, (90°+β−θ) and thethus-refracted light L2 reaches the inclined surface 432 a having anangle of inclination, α, then the incident angle of the refracted lightL2 to the inclined surface 432 a is represented by θ+β−α. The light L3having undergone total reflection on the inclined surface 432 a thenhits the light-emitting surface of he parallel-plate substrate 406 at anincident angle, θ+β−2α. Accordingly, in order that the light L2 havingentered the optical waveguide through its light-entering surface SOundergoes total reflection on the inclined surface 432 a and thenfurther undergoes total reflection also on the light-emitting surfaceand the back surface of the parallel-plate substrate 406, the angle ofinclination, α, of the inclined part 432 must satisfy the formula (6)mentioned below, based on the Snell's law and the total reflectioncondition.

n·sin (θ+β−2α)≧1  (6).

On the other hand, in order that the light L6 running toward thelight-emitting surface of the parallel-plate substrate 406 not havingthe inclined part 432 thereon undergoes total reflection on thelight-emitting surface and the back surface of the parallel-platesubstrate 406, the angle of inclination, β, must satisfy the formula (7)mentioned below, based on the Snell's law and the total reflectioncondition.

n·sin (θ−β)≧1  (7).

Also based on the Snell's law and the total reflection condition on thelight-entering surface SO,

n·sin (90−θ)=1.

Accordingly,

n·cos (θ)=1  (8).

Still on the other hand, in order that the reflected light from thelight having run toward the light-emitting surface of the parallel-platesubstrate 406 not having the inclined part 432 thereon does not againenter the inclined part 432 and that the incident light from thelight-entering surface SO does not hit the inclined surface 432 a twiceor more, the length of inclination, l, of the inclined part 432 mustsatisfy the formula (9) mentioned below. For this, referred to is FIG.72.

l≅h·tan (θ+β)−h·tan (β)  (9).

When the length of the light-entering surface SO is represented by LSO,

LSO≅h/cos (β)+l·tan (α)  (10).

Like in Example 7-1, the optical waveguide 436 is made of an acrylicresin plate (n=1.49) also in this Example. The thickness of the parallelpart of the parallel-plate substrate 406, h=10 mm. From the formula (8),θ=47.84°. Accordingly, from the formula (7), β=5.685°. From the formula(6), the angle of inclination, α=5.685°. From the formulae (9) and (10),the length of inclination l≅12.5 mm; and the length of thelight-entering surface SO, LSO≅11.3 mm.

As compared with a case of using a conventional parallel-plate opticalwaveguide, the width of the open end of the reflector 404 can beincreased also in this Example, like in Example 7-1; and the quantity oflight that may be led into the optical waveguide 436 can be increased by9%, as compared with the conventional case. In addition, the reflector404 can be spaced more from the cold-cathode tube 402 than in theconventional case, to thereby reduce leak current.

In Example 7-1 and Example 7-2, the inclined surfaces 430 a, 432 a areflat. Not limited thereto, the inclined surfaces may be curved or may bepolyhedral. However, in order that all the light having entered theoptical waveguide 436 runs through it, while repeatedly undergoing totalreflection in the remoter area of the parallel-plate substrate nothaving the inclined parts 430, 432 thereon, any light that enters theoptical waveguide through its light-entering surface SO must satisfy thedefined condition for the incident angle. Specifically, the angle ofinclination must not be larger than the defined angle, α, anywhere inthe inclined surfaces 430 a, 432 a.

In Examples 7-1 and 7-2, the structure of the inclined parts 430, 432 isso defined that all the light having entered the optical waveguide doesnot hit the inclined parts twice or more. If desired, however, theirstructure may be so defined that all the light does not hit the inclinedparts three times or more, by prolonging the length of inclination, l.In this case, when the inclined surfaces 430 a, 432 a are flat, thelength of inclination, l, could be up to about 200% of the lengththereof in the above-mentioned Examples.

In addition, the structure may be so defined that the light does not hitthe inclined parts K times or more, by further prolonging the length ofinclination, l. The method for defining the structure in such cases maybe the same as that for defining the structure in which the light doesnot hit the inclined parts three times or more. For example, when theinclined surfaces 430 a, 432 a are flat, the angle of inclination, φ, tobe varied will be about (1/K) times the angle of inclination, α, inExamples 7-1 and 7-2; and the length of inclination, f, to be variedwill be about K times the length of inclination, l, in Examples 7-1 and7-2. Accordingly, φ·f≅α·l.

Example 7-3

Example 7-3 of this embodiment is described with reference to FIG. 73.FIG. 73 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. In this, the same constituent elements as those in Examples 7-1and 7-2 are designated by the same reference numerals, and describingthem is omitted herein. The lighting unit 401 of this Example is similarto but partly differs from that of Example 7-1, and this ischaracterized in that the inclined parts 430,432 as in Example 7-1 aredisposed at the both ends of the parallel-plate substrate 406 oftransparent acrylic resin. The both edges of the parallel-platesubstrate 406 form light-entering surfaces SO, SO′, and light sources434, 434′ are disposed to face the two light-entering surfaces SO, SO′.That is, the light-entering surface SO on the left side in the drawinghas the inclined parts 430, 432 and is equipped with the light source434; and the light-entering surface SO′ on the right side therein hasthe inclined parts 430′, 432′ and is equipped with the light source434′.

The light emitted by the light source 434 enters the optical waveguide436 through the light-entering surface SO, then its optical path isspecifically controlled by the inclined part 430, and thethus-controlled light further runs through the parallel-plate substrate406 while undergoing total reflection therein. On the light-emittingsurface (or the back surface) of the parallel-plate substrate 406 and onthe light-emitting surface (or the back surface) of the inclined surface430 a, diffusion dots or a reflection element, or a refraction element(all not shown) are provided via which the light from the opticalwaveguide 436 is led toward the liquid crystal panel FP. The lightemitted by the light source 434 at one end of the optical waveguide 436runs through the parallel-plate substrate 406 to reach the other end ofthe optical waveguide 436. Since the inclined parts 430′, 432′ are soconstituted that they are open in the light-running direction, the lighthaving reached the other end of the optical waveguide 436 reaches thelight-entering surface SO′, while undergoing total reflection; and apart of it is reflected on the light-entering surface SO′ while theremaining major part thereof enters the light source 434′, and is thenreflected and scattered by the reflector 404′ and the cold-cathode tube402′, and thereafter again enters the optical waveguide 436 though thelight-entering surface SO′. The optical action of the inclined parts430′, 432′ on the re-entered light is the same as that of the inclinedparts 430′, 432′ on the light emitted by the light source 434′, and there-entered light further runs through the optical waveguide 436 in theopposite direction, while also undergoing total reflection therein.

Example 7-4 and Its Modification

Example 7-4 of this embodiment is described with reference to FIG. 74.FIG. 74 is a cross-sectional view showing the outline of the lightingunit 401 of this Example, in which the lighting unit is disposedadjacent to the surface of the liquid crystal panel FP to be illuminatedby it. In this, the same constituent elements as those in Examples 7-1to 7-3 are designated by the same reference numerals, and describingthem is omitted herein. The lighting unit 401 of this Example is similarto but partly differs from that of Example 7-2, and this ischaracterized in that the inclined part 430 (or 432) as in Example 7-2is disposed at the both ends of the parallel-plate substrate 406 oftransparent acrylic resin. In this, the both edges of the parallel-platesubstrate 406 form light-entering surfaces SO, SO′, and light sources434, 434′ are disposed to face the two light-entering surfaces SO, SO′,like in Example 7-3. Concretely, the inclined part 432 stands on theback surface of the parallel-plate substrate 406, extending from thelight-entering surface SO; and the inclined part 432′ stands on the backsurface of the parallel-plate substrate 406, extending from thelight-entering surface SO′. The illumination mode in this Example is thesame as that in Examples 7-2 and 7-3, and describing it is omittedherein.

One modification of this Example is described with reference to FIG. 75.As in FIG. 75, the modification of the lighting unit 401 ischaracterized in that the inclined part 430′ stands on thelight-emitting surface of the parallel-plate substrate 406, extendingfrom the light-entering surface SO′, in place of the inclined part 432′standing on the back surface thereof and extending from thelight-entering surface SO′ in FIG. 74. This modification ensures thesame illumination mode as in Examples 7-2 and 7-3.

Example 7-5 and Its Modification

Example 7-5 of this embodiment is described with reference to FIG. 76Ato FIG. 76C. FIG. 76A is a plan view of the lighting unit of thisExample, showing the optical waveguide 436 seen over the liquid crystalpanel FP. FIG. 76B is a cross-sectional view of FIG. 76A, cut along theline A—A; and FIG. 76C is a cross-sectional view thereof, cut along theline B—B. In these, the same constituent elements as those in Examples7-1 to 7-4 are designated by the same reference numerals, and describingthem is omitted herein. The lighting unit of this Example is similar tobut partly differs from that of Example 7-3 illustrated in FIG. 73, andthis is characterized in that the inclined structure is disposed at allthe four edges of the parallel-plate substrate 406, and that four lightsources 434, 434′, 434″, 434′″ are disposed to face the fourlight-entering surfaces SO, SO′, SO′, SO′″, respectively. Theillumination mode in this Example is the same as that in Examples 7-1and 7-4, and describing it is omitted herein.

One modification of this Example is described with reference to FIG. 77Ato FIG. 77C. FIG. 77A is a plan view of the lighting unit of thisExample, showing the optical waveguide 436 seen over the liquid crystalpanel FP. FIG. 77B is a cross-sectional view of FIG. 77A, cut along theline A—A; and FIG. 77C is a cross-sectional view thereof, cut along theline B—B. The lighting unit 401 of this modification is similar to butpartly differs from that of Example 7-4 illustrated in FIG. 74, and thisis characterized in that the inclined structure is disposed at all thefour edges of the parallel-plate substrate 406. In this, the inclinedparts 430,430′ standing on the light-emitting surface of theparallel-plate substrate 406 are alternated with the inclined parts432,432′ standing on the back surface thereof, in the peripheral regionof the parallel-plate substrate 406. In this constitution, the inclinedparts at the four edges of the optical waveguide 436 are prevented fromoverlapping with each other.

As described in detail with reference to its concrete Examples, thelighting unit of this embodiment ensures increased light-utilizationefficiency, since the open area of the reflector therein, or that is,the area of the light-entering surface SO of the optical waveguidetherein can be enlarged Therefore, this embodiment of the inventionrealizes high-luminance lighting units. In addition, it realizeslow-cost, lightweight and thin lighting units, since the flat part ofthe optical waveguide therein can be thinned.

The lighting unit 401 of the above-mentioned sixth and seventhembodiments is favorable for liquid crystal displays having a liquidcrystal display panel made of two facing substrates with liquid crystalsealed therebetween, serving as a backlight-type lighting unit that isdisposed just below the surface of the liquid crystal display panel tobe illuminated by it.

Eighth Embodiment of the Invention

The visible light source (including fluorescent discharge tubes, orfluorescent discharge tubes equipped with reflectors, etc.) to be usedin the lighting unit of the eighth embodiment of the invention isdescribed with reference to FIG. 78 to FIG. 85. This embodiment relatesto a visible light source in which the UV light generated throughdischarge emission of mercury or the like is led into a phosphor to givevisible light, in particular to cold-cathode tubes favorable as thelight source for lighting units for liquid crystal displays.

For the light source for lighting units for liquid crystal displays,used are cold-cathode tubes for which the inner wall of a glass tube iscoated with a phosphor capable of emitting light in the zone of threeprimary colors. FIG. 78 is an enlarged view showing a part of the crosssection around the wall of a cold-cathode tube 510 mounted onconventional backlight units, cut in the direction perpendicular to theaxial direction of the tube. In the cold-cathode tube 510 illustrated, alayer of phosphor particles 552 dispersed in a binder 554 is fixed onthe inner wall of a glass tube 550 of which the cross sectionperpendicular to the axis of the tube is in the form of a ring.

The cold-cathode tube 510 shown in FIG. 78 has two problems with respectto the light loss in the phosphor 552 fixed on the inner wall of theglass tube 550. First described is the light L1 that goes out of theglass tube 550. The phosphor layer 558 is nearly parallel to the innerwall of the glass tube 550, and has a flat surface. Between the phosphorlayer 558 and the glass tube 550, formed is a space filled withdischarge gas or a vacuum space, 560.

When the light L1 passes through the space 560 and the glass tube 550 togo out of the glass tube 550, a part thereof L2 undergoes totalreflection on the interface between the phosphor layer 558 and the space560 and returns to the phosphor layer 558. The light L3 having passedthrough the region in which the phosphor layer 558 is air tightly bondedto the glass tube 550 also undergoes total reflection on the interfacebetween the inside of the glass tube 550 and the outside thereof. Thelight having returned to the phosphor layer 558 is absorbed by thephosphor 552, but the returned light amounts to about 20% of theintensity of light emission. Therefore, the amount of light emission tothe outside of the glass tube 550 decreases to a non-negligible degree.

Next described is the light L4 from the phosphor 552 toward thedischarge gas layer 556 inside the tube. The surface of the phosphorlayer 558 that faces the discharge gas layer 556 is roughened, dependingon the configuration therearound of the phosphor particles 552 having adiameter of from 3 to 10 μm or so, or many phosphor particles areexposed out of the surface. Therefore, the surface of the phosphor layer558 does not produce reflection (especially total reflection) thereon,and the light L4 easily enters the discharge gas layer 556. However, thelight L4 having entered the discharge gas layer 556 is partly absorbedby the layer 556, and the quantity of light going out of the glass tube550 decreases. For these reasons, the conventional cold-cathode tube isproblematic in that the quantity of light absorbed inside it is largeand is not negligible, and that its luminous efficiency could not beincreased. The object of this embodiment of the invention is to providea discharge emission tube capable of reducing light absorption thereinand capable of realizing increased luminous efficiency.

The discharge emission tube of this embodiment is first characterized inthat the inner surface of the phosphor layer which faces the dischargegas layer therein is so modified that the emitted light hardly entersthe discharge gas layer. Concretely, the surface of the phosphor layerthat faces the discharge gas layer is planarized to have a smoothlycurved surface roughness of at most 10⁻⁷ m or so. With that, thepossibility that the light having been emitted toward the discharge gaslayer undergoes total reflection on the interface between the dischargegas layer and the phosphor layer is increased, and, as a result, theabsorption of light by the discharge gas layer can be thereby reduced.

The second characteristic is that the outer surface of the phosphorlayer which faces the inner wall of the glass tube is so modified thatthe emitted light easily goes out of the tube. Concretely, the phosphorlayer is so processed that the phosphor particles are exposed out of itsouter surface which faces the inner wall of the glass tube, whereby thepossibility that the light running out of the tube undergoes totalreflection on the interface between the phosphor layer and the space oron the outer wall of the glass tube is reduced.

Apart from it, the binder for binding the phosphor particles is soprocessed that the outer surface of the phosphor layer which faces theinner wall of the glass tube is roughened to have a profile similar tothe phosphor particles and their configuration. With that, thepossibility that the light running out of the tube undergoes totalreflection on the interface between the phosphor layer and the space oron the outer wall of the glass tube is reduced.

The third characteristic is that a phosphor layer is formed on the outerwall of the glass tube. The advantage of the phosphor layer formed onthe outer wall of the glass tube is that its surface that receives UVrays is readily planarized and smoothly curved.

The fourth characteristic is that the plane accuracy of the surface ofthe phosphor layer which faces the discharge gas layer is on the levelof the visible light wavelength range. With that, light scattering onthe interface between the discharge gas layer and the phosphor layer isreduced, and the light to return from the phosphor layer to thedischarge gas layer is reduced.

The fifth characteristic is that the visible light source comprises aphosphor layer and a UV source spaced from each other and that thesurface thereof through which the visible light goes out of it isroughened. That is, the visible light source comprising a phosphor layerand a UV source is so constituted that the visible light converted inthe phosphor layer is taken out of it through one surface of thephosphor layer and that the surface of the phosphor layer through whichthe visible light is taken out of it is roughened in accordance with theprofile of the phosphor particles.

The sixth characteristic of the visible light source is that the surfaceof the phosphor layer which faces the UV source therein is planarized.Concretely, the surface of the phosphor layer nearer to the UV source isplanarized to have a surface roughness of at most 10⁻⁷ m or so.

The visible light source of this embodiment is described more concretelywith reference to the following Examples.

Example 8-1

Referring to FIG. 79 and FIG. 80, Example 8-1 of this embodiment isdescribed. FIG. 79 is a cross-sectional view of the cold-cathode tube ofExample 8-1, cut in the direction perpendicular to the axial directionof the tube. The cold-cathode tube 450 comprises a combination of anouter transparent tube 452 of hard glass having, for example, an outerdiameter of 2.8 mm and an inner diameter of 2.6 mm; and an innertransparent tube 458 of quartz having, for example, an outer diameter of2.4 mm and an inner diameter of 2.0 mm. The outer wall of the inner tube458 has a phosphor layer 456 formed thereon. The phosphor layer 456comprises phosphor particles 462 and a binder 464 that carries themdispersed therein. The inner tube 458 surrounds a hollow, which isfilled with a discharge gas to form a discharge gas layer 460.

In this embodiment, the phosphor layer 456 adheres to the outer wall ofthe inner tube 458, and the interface between them is a smoothly curvedand planarized plane. Accordingly, the surface of the phosphor layer 456that faces the discharge gas layer 460 is planarized. On the otherhand,the outer surface of the phosphor layer 456 opposite to the dischargegas layer 460 is not kept in contact with the inner wall surface of theouter tube 452, and the phosphor particles 462 are exposed out of theouter surface of the phosphor layer 456. Therefore, the outer surface ofthe phosphor layer 456 is roughened, and its surface roughness is nearlyto the degree of the radius of the phosphor particles 462 (about 1.5 to5 μm) and follows the configuration of the phosphor particles 462.

The phosphor layer 456 in this Example is formed in the manner mentionedbelow. First prepared is a coating liquid of phosphor. That is, amixture of phosphor particles 462 in 5% by volume of a binder (waterglass) 464 is dispersed in a solvent of 0.6% by weight of ammoniumpolymethacrylate in water to prepare a coating liquid of phosphor. Thecoating liquid is applied to a quartz tube (inner tube 458) standingvertically, along its outer wall surface, then the resulting quartz tubeis baked, and the phosphor layer 456 formed around it is dried with hotair.

The inner structure of the thus-formed phosphor layer 456 is analyzed.In a conventional case, the binder 464 air tightly fills the spacearound a large number of nearly spherical phosphor particles 462 to forma dense film. In this Example, however, the binder 464 is not enough tofully fill the space around the phosphor particles 462. Therefore, thefine hillocks in the outer surface of the quartz tube (inner tube 458)act as nuclei for film formation, and the water glass deposits on themto form a film. As a result, the interface between the quartz tube andthe film has a dense structure. However, in the area remoter from thesurface of the quartz tube, the water glass is not enough for dense filmformation, and the space around the phosphor particles 462 is not fullyfilled with the water glass. Finally, therefore, the surface of thephosphor layer 456 not in contact with the quartz tube is roughened onan order of a few μm, directly reflecting the outer profile of thephosphor particles 462 and the configuration thereof.

FIG. 80 is a view showing a part of the cross section around the wall ofthe cold-cathode tube 450, cut in the direction perpendicular to theaxial direction of the tube. Referring to FIG. 80, the optical path ofthe light emitted by the cold-cathode tube 450 is described. A space 454is formed between the surface of the phosphor layer 456 opposite to thedischarge gas layer 460 and the inner wall of the outer tube 452. Thelight having run through the space 454 and entered the outer tube 452 ata point P of the inner wall thereof is refracted, and the refractedlight L1 then further runs inside the outer tube 452 and goes out of itthrough the outer wall thereof. The refractive index of the outer tube452 is larger than that of the space 454.

Next described is the light running from the phosphor particles 462toward the inner wall of the outer tube 452. The surface of the phosphorlayer 456 that faces the inner wall of the outer tube 452 is roughened,following the phosphor particles 462 and their configuration, and somephosphor particles 462 (not shown). Accordingly, the light havingreached the surface of the phosphor layer 456 just below the inner wallof the outer tube 452 is hardly reflected thereon, and the light L2easily passes through the outer tube 452. In this region, only a part ofthe emitted light that is nearly parallel to the inner wall of the outertube 452, like the light L3, undergoes total reflection on the interfacebetween the surface of the phosphor layer 456 and the space 454, and,therefore, most of the emitted light can be led out of the outer tube452 at high efficiency.

Next described is the light running toward the discharge gas layer 460.The phosphor layer 456 is nearly parallel to the inner wall of the innertube 458 and has a smooth surface. Therefore, a part of the lightemitted by the phosphor particles 462 undergoes total reflection on theinterface between the phosphor layer 456 and the inner tube 458, andreturns to the phosphor layer 456. This is the returned light L4. On theother hand, the light having entered the inner tube 458 undergoes totalreflection on the interface between the inner tube 458 and the dischargegas layer 460, and returns to the inner tube 458. This is the returnedlight L5. Accordingly, only apart, L6, of the light emitted by thephosphor particles 462 toward the discharge gas layer 460 enters thedischarge gas layer 460.

In this Example, since the inner surface of the phosphor layer 456 thatsurrounds the inner tube 458 and faces the discharge gas layer 460 isplanarized in the manner as described hereinabove, the possibility thatthe light emitted toward the discharge gas layer 460 undergoes totalreflection on the interface between the phosphor layer 456 and the innertube 458 and also on the interface between the inner tube 458 and thedischarge gas layer 460 is increased, and the absorption of light by thedischarge gas layer 460 is reduced. In addition, since the phosphorlayer 456 is formed to surround the outer wall of the inner tube 458,the surface of the phosphor layer 456 that receives UV rays can bereadily planarized.

Moreover, in this Example, some phosphor particles 462 are exposed outof the outer surface of the phosphor layer 456 that faces the inner wallof the outer tube 452, and the outer surface of the phosphor layer 456is roughened so as to nearly follow the profile of the phosphorparticles 462 themselves and their configuration. Therefore, thepossibility that the light running toward the outer tube 452 and outsideit undergoes total reflection on the interface between the phosphorlayer 456 and the space 454, or in the space 454 and on the inner andouter walls of the outer tube 452 is reduced.

In addition, in this Example, the surface of the phosphor layer 456 thatfaces the discharge gas layer 460 is so planarized that its planeaccuracy is on the level of the visible light wavelength range, forexample, on the level of surface roughness of at most about 10⁻⁷ m. Withthat, the light to scatter in the interface between the discharge gaslayer 460 and the phosphor layer 456 is reduced and the light to returnfrom the phosphor layer 456 to the discharge gas layer 460 is reduced.

Table 4 below shows the comparison between the cold-cathode tube 450 ofthis Example and a conventional cold-cathode tube in point of lighttransmission, absorption and reflection. As is obvious from the data inTable 4, the cold-cathode tube of this Example is superior to theconventional cold-cathode tube with respect to all the parameters ofvisible light transmittance, absorbance and reflectance.

TABLE 4 Comparison between Cold-Cathode Tube 450 of Example 8-1 andConventional Cold-Cathode Tube Visible Light Visible Light Visible LightTransmittance Absorbance Reflectance Conventional Cold-Cathode 14% 40%46% Tube Cold-Cathode Tube 450 of 76% 15%  9% Example 8-1

Example 8-2

Example 8-2 of this embodiment is described with reference to FIG. 81and FIG. 82. FIG. 81 is a cross-sectional view of the visible lightsource 470 of Example 8-2, cut in the direction perpendicular to theaxial direction of the UV source. For the UV source, used is a mercurydischarge tube 472 of which the bulb is a quartz tube. The mercurydischarge tube 472 has an outer diameter of 2.6 mm and an inner diameterof 2.0 mm. The mercury discharge tube 472 is covered with a concavemirror 474 of aluminium, except for the region of its open end. For itscross section, the mirror surface of the concave mirror 474 issemicircular, having a radius, r, to its center that corresponds to thepoint, P, on the outer surface of the mercury discharge tube 472, r=4mm. To the open end of the concave mirror 474, attached is an emissionfilter 476 having a substrate of hard glass.

FIG. 82 is an enlarged view showing the details of the constitution ofthe emission filter 476. As in FIG. 82, the surface of the hard glasssubstrate 480 that faces the mercury discharge tube 472 is coated with aphosphor layer 478, and the opposite surface thereof is coated with anUV reflection film 482.

In the phosphor layer 478, a large number of phosphor particles 486 arefixed by a binder 488. The surface of the phosphor layer 478 that facesthe hard glass substrate 480 is roughened, and this is kept in contactwith the substrate 480 via the space 484 therebetween. Some phosphorparticles (having a diameter of from 3 μm to 10 μm) are exposed out toroughen the surface of the phosphor layer 478.

The phosphor layer 478 in this Example is formed in the manner mentionedbelow. First prepared is a coating liquid of phosphor. Concretely, amixture of phosphor particles 486 in 35% by volume of a binder (waterglass) 488 is dispersed in a solvent of 0.6% by weight of ammoniumpolymethacrylate in water to prepare a coating liquid of phosphor. Onthe other hand, a film of a water-repellent substance is formed on thesurface of the hard glass substrate 480 to be coated with phosphor. Thefilm-forming substance is a metal fluoride. In this Example, magnesiumfluoride is used. According to a pulling method, the coating liquid isapplied to the magnesium fluoride-coated surface of the hard glasssubstrate 480, then the hard glass substrate 480 is baked, and thephosphor film 478 formed thereon is dried with hot air.

The inner structure of the thus-formed phosphor layer 478 is analyzed.The space around the nearly spherical phosphor particles 486 is filledwith the binder 488 to form a dense film. As compared with the phosphorlayer 456 in Example 8-1, the phosphor layer 478 in this Examplecontains a larger amount of water glass, and the space around thephosphor particles 486 is fully filled with the water glass to form sucha dense film. However, since the surface of the hard glass substrate 480has a film of a water-repellent substance formed thereon, the coatingliquid can not fully wet it, and, as a result, the phosphor layer 478 isformed on the hard glass substrate 480 with some non-contact spacetherebetween. In the non-contact space between the phosphor layer 478and the hard glass substrate 480, the surface of the phosphor layer 478that faces the substrate 480 is roughened, reflecting the outer profileof the phosphor particles 486 themselves and their configuration.

In that manner, this Example differs from Example 8-1. Specifically, inthis, the phosphor layer 478 is spaced from the mercury discharge tube472, and the phosphor layer 478 is so disposed that its roughenedsurface faces the light emission side. On the other hand, the surface ofthe phosphor layer 478 that faces the mercury discharge tube 472 isplanarized to have a surface roughness of at most about 10⁻⁷ m or so.Accordingly, the constitution of this Example ensures high-efficiencylight emission, like that of Example 8-1.

Example 8-3

Example 8 -3 of this embodiment is described with reference to FIG. 83to FIG. 85. FIG. 83 is a cross-sectional view of the visible lightsource of this Example, cut in the direction perpendicular to the axialdirection of the UV source. For the UV source, used is a mercurydischarge tube 490 of which the bulb is a quartz tube, like in Example8-2. Around the mercury discharge tube 490, disposed is an aluminummirror 492 having an angular U-shaped cross section. Adjacent to theopen end of the aluminum mirror 492, fixed is an optical waveguide 600via a UV reflection film 602 therebetween. On a part of the innerreflective surface of the aluminum mirror 492 having an angular U-shapedcross section, a phosphor layer 494 is formed opposite to the open endof the aluminum mirror 492. As in FIG. 84, the phosphor layer 494 is airtightly formed on the inner surface of the aluminum mirror 492, and alarge number of phosphor particles 496 are fixed by a binder 498 in thephosphor layer 494. The surface of the phosphor layer 494 opposite tothe inner surface of the aluminum mirror 492 is roughened to have asurface roughness of from 5 to 10 μm. The phosphor layer 494 in thisExample may be formed in the same manner as in Example 8-1.

A phosphor layer 494 is also formed on a part of the outer surface ofthe mercury discharge tube 490. The phosphor layer 494 on the outersurface of the mercury discharge tube 490 is formed within the regionbetween the two points at which the tangential lines drawn from theupper and lower corners of the angular U-shaped cross section of thealuminum mirror 492 toward the outer surface of the mercury dischargetube 490 each meet the outer surface of the mercury discharge tube 490.FIG. 85 is an enlarged view showing the details of a part of thephosphor layer 494 formed on the outer surface of the mercury dischargetube 490. As illustrated, the constitution of the phosphor layer 494formed on the outer surface of the mercury discharge tube 490 is thesame as that of the phosphor layer 494 formed on the inner surface ofthe aluminum mirror 492.

The light from the phosphor layer 494 on the outer surface of themercury discharge tube 490 does not reach the phosphor layer 494 formedon the inner surface of the aluminum mirror 492. In the constitution ofthis Example, therefore, the light that may enter the phosphor layer 494twice or more is reduced, and the visible light loss (this amounts 20%in one re-entrance of light into the phosphor layer) is thereby reduced.Accordingly, the electric power-visible light conversion efficiency inthe constitution of this Example is high.

Table 5 below shows a comparison between the visible light source ofthis Example and a conventional light source in point of the lightemission efficiency. As is obvious from the data in Table 5, the visiblelight source of this Example is superior to the conventional visiblelight source with respect to the overall efficiency. The principledefficiency in conversion of UV light into visible light is the same inthe two, and is therefore neglected herein.

TABLE 5 Comparison between Visible Light Source of Example 8-3 andConventional Light Source in point of Light Emission Efficiency LightEmission A from Efficiency B of Light Overall Emission Tube Source Unit(except Efficiency (UV emission = 1) the emission tube) A × B VisibleLight 100% 63% 63% Source of Example 8-3 Conventional  73% 75% 54% LightSource

As described in detail hereinabove, the invention realizeshigh-luminance and long-life light sources ensuring uniform emission,and realizes not only display devices favorable to flat panel displayssuch as liquid crystal displays, etc. but also lighting devices for theuse of the signboard and the like.

What is claimed is:
 1. A lighting unit comprising: a light source unithaving an emitter which has a transparent body with a refractive indexn0 containing a light-emitting substance sealed in an empty regioninside thereof, a housing that houses the emitter and has reflectorformed on an inner surface, and a transparent filler with a refractiveindex n1 filled in the housing; and an optical waveguide made of atransparent substance with a refractive index n2 and having alight-emitting surface; wherein the profile of the light-reflectingsurface of the reflector satisfies the requirement of:|θ1—θ2|<cos⁻¹(1/n2), in which θ1 indicates the angle between the normalline nA at a point A on the surface and the tangential line 1 thattangentially connects the point A and the outline of the empty region,and θ2 indicates the angle between the line segment m that is parallelto the light-emitting surface and is in the plane formed by the normalline nA and the tangential line 1, and the normal line nA.
 2. A lightingunit comprising: a light source unit having an emitter which has atransparent body with a refractive index n0 containing a light-emittingsubstance sealed in an empty region inside thereof, a housing thathouses the emitter and has a reflector formed on an inner surface, atransparent filler with a refractive index n1 filled in the housing, andan optical path-changing device disposed in the transparent filler forchanging an optical path; and an optical waveguide made of a transparentsubstance with a refractive index n2 and having a light-emittingsurface.
 3. A lighting unit comprising: a light source unit having anemitter which has a transparent body with a refractive index n0containing a light-emitting substance sealed in an empty region insidethereof, a housing that houses the emitter and has a reflector formed onits inner surface, and a transparent filler with a refractive index n1filled in the housing; an optical waveguide made of a transparentsubstance with a refractive index n2 and having a light-emittingsurface; a second reflector formed on the light-emitting surface andhaving a plurality of open ends; a second light source unit, whereineach light source unit is provided at an end of the optical waveguide,wherein a distance, w, between the light source units that correspondsto the length of the optical waveguide sandwiched between the lightsource units and a thickness, d, of the optical waveguide satisfy therequirement of 20×d<w<45×d.
 4. The lighting unit as claimed in claim 1,wherein the emitter is a discharge tube; and the dielectric loss tangentof the transparent filler is minimized at around the driving frequencyof the discharge tube.
 5. The lighting unit as claimed in claim 1,wherein the emitter is a discharge tube; and the dielectric constant ofthe transparent filler has a maximum value at around the drivingfrequency of the discharge tube.
 6. The lighting unit as claimed inclaim 1, wherein the refractive index n1 of the transparent filler fallsbetween the refractive index n0 of the transparent body that forms theemitter and the refractive index n2 of the optical waveguide.
 7. Aliquid crystal display with a liquid crystal sandwiched between a pairof two facing substrates, which comprises: a lighting unit comprising: alight source unit having an emitter which has a transparent body with arefractive index n0 containing a light-emitting substance sealed in anempty region inside thereof, a housing that houses the emitter and hasreflector formed on an inner surface, and a transparent filler with arefractive index n1 filled in the housing; and an optical waveguide madeof a transparent substance with a refractive index n2 and having alight-emitting surface; wherein the profile of the light-reflectingsurface of the reflector satisfies the requirement of:|θ1−θ2<cos⁻¹(1/n2), in which θ1 indicates the angle between the normalline nA at a point A on the surface and the tangential line 1 thattangentially connects the point A and the outline of the empty region,and θ2 indicates the angle between the line segment m that is parallelto the light-emitting surface and is in the plane formed by the normalline nA and the tangential line 1, and the normal line nA.
 8. A lightingunit comprising: a plurality of optical waveguides disposed adjacent toa display panel surface to be illuminated; an emission tube disposedbetween the optical waveguides and nearer to the back surfaces of theoptical waveguides than to the light-emitting surfaces thereof that facethe display panel surface; and a reflector is disposed between theneighboring optical waveguides in the space between the display surfaceand the emission tube.
 9. A lighting unit comprising: a plurality ofoptical waveguides disposed adjacent to a display panel surface to beilluminated; and an emission tube disposed between the opticalwaveguides and nearer to the back surfaces of the optical waveguidesthan to the light-emitting surfaces thereof that face the display panelsurface; wherein a light-entering surface of each optical waveguide atan end meets the back surface thereof at an obtuse angle.
 10. Thelighting unit as claimed in claim 9, wherein each optical waveguide ismade of a transparent member having a refractive index, n=1.41 or more;and the obtuse angle is larger than 90° but not larger than 102°. 11.The lighting unit as claimed in claim 9, further comprising a reflectordisposed adjacent to the emission tube on the side thereof opposite tothe display panel surface.
 12. The lighting unit as claimed in claim 9,further comprising a light-scattering element disposed between theneighboring optical waveguides in the space between the display panelsurface and the emission tubes.
 13. The lighting unit as claimed inclaim 12, wherein the light-scattering element is an anisotropiclight-scattering element of which the light-diffusing ability variesdepending on the direction of an entering light.
 14. The lighting unitas claimed in claim 8, further comprising a diffuser disposed on thesurface of each optical waveguide.
 15. The lighting unit as claimed inclaim 14, wherein the diffuser is a diffusion pattern of a plurality ofdiffusion dots disposed on the back surface of each optical waveguide.16. The lighting unit as claimed in claim 14, wherein the diffuser is aplurality of recesses each having a triangular cross section, formed onthe back surface of each optical waveguide.
 17. The lighting unit asclaimed in claim 14, further comprising; a second optical waveguide; andan optical adhesive layer provided between the surfaces of the pluralityof optical waveguides and the second optical waveguide.
 18. The lightingunit as claimed in claim 17, wherein the diffuser is attached to thesecond optical waveguide and not to the plurality of optical waveguides.19. A liquid crystal display comprising a liquid crystal panel withliquid crystal sealed between two facing substrates, and a lighting unitdisposed adjacent to the surface of the liquid crystal panel to beilluminated by the unit, wherein the lighting unit comprises: aplurality of optical waveguides disposed adjacent to a display panelsurface to be illuminated; an emission tube disposed between the opticalwaveguides and nearer to the back surfaces of the optical waveguidesthan to the light-emitting surfaces thereof that face the display panelsurface; and a reflector is disposed between the neighboring opticalwaveguides in the space between the display surface and the emissiontube.
 20. A liquid crystal display comprising a liquid crystal panelwith liquid crystal sealed between two facing substrates, and a lightingunit disposed adjacent to the surface of the liquid crystal panel to beilluminated by the unit, wherein the lighting unit comprises: aplurality of optical waveguides disposed adjacent to a display panelsurface to be illuminated; and an emission tube disposed between theoptical waveguides and nearer to the back surfaces of the opticalwaveguides than to the light-emitting surfaces thereof that face thedisplay panel surface; wherein a light-entering surface of each opticalwaveguide at an end meets the back surface thereof at an obtuse angle.21. A liquid crystal display with a liquid crystal sandwiched between apair of two facing substrates, which comprises: a lighting unitcomprising: a light source unit having an emitter which has atransparent body with a refractive index n0 containing a light-emittingsubstance sealed in an empty region inside thereof, a housing thathouses the emitter and has a reflector formed on an inner surface, atransparent filler with a refractive index n1 filled in the housing, andan optical path-changing device disposed in the transparent filler forchanging an optical path; and an optical waveguide made of a transparentsubstance with a refractive index n2 and having a light-emittingsurface.
 22. A liquid crystal display with a liquid crystal sandwichedbetween a pair of two facing substrates, which comprises: a lightingunit comprising: a light source unit having an emitter which has atransparent body with a refractive index n0 containing a light-emittingsubstance sealed in an empty region inside thereof, a housing thathouses the emitter and has a reflector formed on its inner surface, anda transparent filler with a refractive index n1 filled in the housing;an optical waveguide made of a transparent substance with a refractiveindex n2 and having a light-emitting surface; and a second reflectorformed on the light-emitting surface and having a plurality of openends; a second light source unit, wherein each light source unit isprovided at an end of the optical waveguide, wherein a distance, w,between the light source units that corresponds to the length of theoptical waveguide sandwiched between the light source units and athickness, d, of the optical waveguide satisfy the requirement of20×d<w<45×d.